U.S. patent application number 12/779163 was filed with the patent office on 2010-12-02 for fixing device and image forming apparatus including fixing device.
Invention is credited to Hiroyuki Kageyama, Tetsunori MITSUOKA, Akihiko Taniguchi.
Application Number | 20100303525 12/779163 |
Document ID | / |
Family ID | 43220388 |
Filed Date | 2010-12-02 |
United States Patent
Application |
20100303525 |
Kind Code |
A1 |
MITSUOKA; Tetsunori ; et
al. |
December 2, 2010 |
FIXING DEVICE AND IMAGE FORMING APPARATUS INCLUDING FIXING
DEVICE
Abstract
A fixing device of belt fixing type is provided. A heat
generating member that is a heat generating source for heating a
fixing belt has a heat generating layer composed of a resistance
heat generating element that generates heat due to being energized.
The resistance heat generating element includes a paper passing
region heating section and a detecting section provided on an end
portion in an axial direction of the heat generating member and
electrically connected in parallel with the paper passing region
heating section. Furthermore, in a vicinity of the detecting
section, an overheat preventing element that suppresses
energization to the resistance heat generating element when
temperature of the detecting section reaches a predetermined value,
is provided.
Inventors: |
MITSUOKA; Tetsunori; (Osaka,
JP) ; Taniguchi; Akihiko; (Osaka, JP) ;
Kageyama; Hiroyuki; (Osaka, JP) |
Correspondence
Address: |
MARK D. SARALINO ( SHARP );RENNER, OTTO, BOISSELLE & SKLAR, LLP
1621 EUCLID AVENUE, 19TH FLOOR
CLEVELAND
OH
44115
US
|
Family ID: |
43220388 |
Appl. No.: |
12/779163 |
Filed: |
May 13, 2010 |
Current U.S.
Class: |
399/329 |
Current CPC
Class: |
G03G 2215/2029 20130101;
G03G 15/2039 20130101 |
Class at
Publication: |
399/329 |
International
Class: |
G03G 15/20 20060101
G03G015/20 |
Foreign Application Data
Date |
Code |
Application Number |
May 26, 2009 |
JP |
2009-127065 |
Claims
1. A fixing device comprising: a first fixing member; a heating
member; a fixing belt that forms an endless-shaped belt member
supported around the first fixing member and the heating member
with tension to be rotatable, and comes into contact with the
heating member to be heated; and a second fixing member that forms
a fixing nip region together with the fixing belt, the fixing
device fixing a toner image borne on a recording medium onto the
recording medium in the fixing nip region under application of heat
and pressure, the heating member including: a curved heat radiating
member having an outer circumferential surface in contact with the
fixing belt; and a heat generating member having a heat generating
layer composed of a resistance heat generating element that
generates heat due to being energized and arranged to be in contact
with an inside surface of the heat radiating member, the resistance
heat generating element including: a paper passing region heating
section forming a heat generating source part for heating a paper
passing region of the fixing belt where the recording medium
contacts and passes in the fixing nip region; and a detecting
section that is provided to correspond to a paper non-contacting
region of the recording medium of the fixing belt and connected
electrically in parallel with the paper passing region heating
section, and the fixing device further comprising an overheat
preventing element that is provided in a vicinity of the detecting
section and suppresses energization to the resistance heat
generating element when temperature of the detecting section
reaches a predetermined value.
2. The fixing device of claim 1, wherein the paper passing region
heating section and the detecting section have an equivalent power
density.
3. The fixing device of claim 1, wherein the paper passing region
heating section and the detecting section have an equivalent
temperature rising speed in generating heat due to being
energized.
4. The fixing device of claim 1, wherein the paper passing region
heating section and the detecting section have an equivalent
specific heat capacity.
5. The fixing device of claim 1, wherein the resistance heat
generating element is configured to form a surface of a fixed shape
as a whole.
6. The fixing device of claim 1, wherein the resistance heating
element is a ceramic heating element.
7. The fixing device of claim 1, wherein the resistance heating
element has a positive resistance-temperature property in which, as
temperature rises, electrical resistance increases.
8. The fixing device of claim 1, wherein the resistance heating
element has a negative resistance-temperature property in which, as
temperature rises, electrical resistance decreases.
9. The fixing device of claim 1, wherein the resistance heating
element has a positive resistance-temperature property and a
negative resistance-temperature property.
10. The fixing device of claim 1, wherein the heat generating
member has a heat generating layer composed of a plurality of the
resistance heat generating elements, and is configured such that a
heat generating part that generates heat due to being energized is
divided into more than one, each of the plurality of resistance
heat generating elements has the paper passing region heating
section and the detecting section.
11. The fixing device of claim 1, wherein the second fixing member
includes a pressure belt that is an endless-shape belt member
supported around a pressure member and a supporting member with
tension so as to be rotatable, and the pressure member is provided
to face the first fixing member with the fixing belt and the
pressure belt interposed therebetween.
12. A fixing device of two-stage fixing type, comprising: a first
fixing section that performs primary fixing of a toner image borne
on a recording medium to be conveyed onto the recording medium
under application of heat and pressure; and a second fixing section
that is arranged on a downstream side of a conveyance direction of
the recording medium with respect to the first fixing section, and
performs secondary fixing of the toner image after the primary
fixing onto the recording medium under application of heat and
pressure, the first fixing section and the second fixing section
being the fixing device of claim 1.
13. A fixing device of two-stage fixing type, comprising: a first
fixing section that performs primary fixing of a toner image borne
on a recording medium to be conveyed onto the recording medium
under application of heat and pressure; and a second fixing section
that performs secondary fixing of the toner image after the primary
fixing onto the recording medium under application of heat and
pressure, the second fixing section being configured by a pair of
heating and pressure rollers that are provided with a heating
section in an interior thereof, and are in pressure-contact with
each other, and being arranged on a downstream side of a conveyance
direction of the recording medium with respect to the first fixing
section, and the first fixing section being the fixing device of
claim 1.
14. An image forming apparatus including the fixing device of claim
1.
15. An image forming apparatus including the fixing device of claim
12.
16. An image forming apparatus including the fixing device of claim
13.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to Japanese Patent
Application No. 2009-127065, which was filed on May 26, 2009, the
contents of which are incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a fixing device that fixes
a toner image onto a recording medium by an action of heat and
pressure, and to an image forming apparatus including the fixing
device.
[0004] 2. Description of the Related Art
[0005] As a fixing device for use in an electrophotographic image
forming apparatus such as a copying machine and a printer, a fixing
device of heat-roller fixing type has been in wide use. The fixing
device of heat-roller fixing type includes a pair of rollers (a
fixing roller and a pressure roller) that are brought into contact
with each other under pressure. By means of a heating section
composed for example of a halogen lamp, which is placed in each of
or one of the pair of rollers interiorly thereof, the pair of
rollers are heated to a predetermined temperature (a fixing
temperature). With the pair of rollers kept in a heated state, such
as a recording paper sheet, which is a recording medium having
formed thereon an unfixed toner image, is fed to a region where the
pair of rollers make pressure-contact with each other (a fixing nip
region). Upon the recording paper sheet passing through the
pressure-contact region, the toner image is fixed to the recording
paper sheet under application of heat and pressure.
[0006] Incidentally, a fixing device for use in a color image
forming apparatus generally employs an elastic roller constructed
by forming an elastic layer made for example of silicone rubber on
a surface layer of the fixing roller. By designing the fixing
roller as an elastic roller, it is possible for the surface of the
fixing roller to become elastically deformed so as to conform to
irregularities of the unfixed toner image, wherefore the fixing
roller makes contact with the toner image so as to cover the
surface of the toner image. This makes it possible to perform
satisfactory thermal fixing on the unfixed color toner image that
is larger in toner adherent amount than a monochromatic toner
image. Moreover, by virtue of a deflection-releasing effect exerted
by the elastic layer in the fixing nip region, it is possible to
provide enhanced releasability for a color toner that is more
susceptible to occurrence of offset than a monochromatic toner.
Further, since the fixing nip region is convexly curved in a
radially-outward direction so as to define a so-called reverse nip
configuration, it is possible to attain higher paper-stripping
capability. That is, a paper stripping action can be produced
without using a stripping portion such as a stripping pawl
(self-stripping action), wherefore image imperfection caused by the
provision of the stripping portion can be eliminated.
[0007] Incidentally, in such a fixing device provided in a color
image forming apparatus, it is necessary to make a nip width of the
fixing nip region wide in order to correspond to increase in speed.
One available method of increasing the fixing nip width is to
increase the thickness of the elastic layer of the fixing roller
and the diameter of the fixing roller. However, in a fixing roller
having an elastic layer, the elastic layer can not sufficiently
conduct heat, thus, in a case where a heating section is provided
inside the fixing roller, there is a problem that a temperature of
the fixing roller is not followed when a process speed is
increased. On the other hand, when a diameter of the fixing roller
is increased, there is a problem that it takes longer time to warm
up or power consumption is increased.
[0008] As a fixing device provided in a color image forming
apparatus to solve such problems, Japanese Unexamined Patent
Publication JP-A 10-307496 (1998) discloses a fixing device of belt
fixing type that is configured so that a fixing belt is supported
around a fixing roller and a heating roller, and the fixing roller
and a pressure roller are brought into pressure-contact with each
other with the fixing belt interposed therebetween. In the fixing
device of belt fixing type, since the fixing belt with a small heat
capacity is heated, it takes short time to warm up and it is not
necessary to incorporate a heat source such as a halogen lamp in
the fixing roller, thus making it possible to provide a thick
elastic layer with low hardness made of sponge rubber and the like
and to secure a wide nip width.
[0009] Furthermore, JP-A 2002-333788 discloses a fixing device of
planar heat generating belt fixing type with a heating section as a
planar heat generating element. In the fixing device of planar heat
generating belt fixing type, when a heat capacity of the heating
section is reduced, the planar heat generating element as the
heating section directly generates heat at the same time, thus a
thermal response speed is also enhanced compared to a system in
which a heating roller is heated indirectly using a halogen lamp or
the like and it is possible to attain further shortening of a time
for warm up and more energy saving.
[0010] When the planar heat generating element composed of a
resistance heat generating element including a metal and an
inorganic substance is separated or risen from a substrate, there
is a possibility that the planar heat generating element becomes an
overheated state and results in smoke generation or burnout.
Therefore, in the fixing device of planar heat generating belt
fixing type, temperature abnormality under which the planar heat
generating element becomes the overheated state is detected by an
overheat preventing element (thermostat, thermal fuse, thermal
protector, or the like), energization to the planar heat generating
element is cut off based on the detection result, and thereby it is
possible to prevent that the planar heat generating element becomes
the overheated state and results in smoke generation or
burnout.
[0011] In the fixing device of belt fixing type using the planar
heat generating element of high power density, since the
temperature rising speed of the planar heat generating element is
high, in order to prevent that the planar heat generating element
becomes the overheated state and results in smoke generation or
burnout, the temperature abnormality under which the planar heat
generating element becomes the overheated state should be detected
earlier. In order to detect earlier the temperature abnormality
under which the planar heat generating element becomes the
overheated state, the overheat preventing element may be arranged
to be in contact with the fixing belt or the planar heat generating
element, however, in such a case, there is a possibility that not
only a defect occurs in the fixed image on recording paper, but
also temperature distribution on the surface of the fixing belt
becomes non-uniform. Furthermore, when the overheat preventing
element is arranged to be in contact with the fixing belt or the
planar heat generating element, there is a possibility that
detection sensitivity of the overheat preventing element becomes
poor and thereby the thermal abnormality itself is not possible to
be detected.
[0012] Moreover, in the fixing device of planar heat generating
belt fixing type, a width of a paper non-passing region on the
fixing belt surface varies depending on a size of the recording
paper to be supplied to the fixing nip region. In the paper
non-passing region that the recording paper does not contact on the
surface of the fixing belt, since heat generated from the planar
heat generating element will not be taken by the recording paper, a
regional part of the planar heat generating element corresponding
to the paper non-passing region becomes an excessive temperature
rising state. In this way, when the planar heat generating element
becomes the excessive temperature rising state regionally
corresponding to the paper non-passing region, there is a case
where the overheat preventing element that detects overheated state
of the planar heat generating element operates erroneously.
[0013] To solve the above problem, Japanese Unexamined Patent
Publication JP-A 2003-280413 discloses a heating device composed of
a resistance heat generating element that generates heat due to
being energized, including a paper passing portion corresponding to
a paper passing region of recording paper and a paper non-passing
portion which is a region part other than the paper passing portion
and to which a thermo-protector (overheat preventing element) is
arranged in a vicinity thereof, and the paper passing portion and
the paper non-passing portion are electrically connected in
series.
[0014] In a case where the heating apparatus disclosed in JP-A
2003-280413 is used as a heating section that heats the fixing belt
in the fixing device of belt fixing type, overheated state of the
paper passing portion is indirectly detected by temperature change
in the paper non-passing portion of the resistance heat generating
element due to energization, when the temperature in the paper
non-passing portion reaches a predetermined temperature, it is
possible that the thermo-protector cuts off the energization. That
is, by using the heating apparatus disclosed in JP-A 2003-280413 as
a heating section that heats the fixing belt, irrespective of the
size of the recording paper to be supplied to the fixing nip
region, the overheated state of the paper passing portion is able
to be indirectly detected by the temperature change in the paper
non-passing portion of the resistance heat generating element
corresponding to the paper non-passing region that the recording
paper does not contact all the time, it is possible to prevent that
the overheat preventing element operates erroneously.
[0015] However, in the heating apparatus disclosed in JP-A
2003-280413, it is configured that the paper passing portion and
the paper non-passing portion of the resistance heat generating
element that generates heat due to being energized are electrically
connected in series, when power of the paper passing portion and
the paper non-passing portion is set to be the same, power density
of the paper non-passing portion is smaller than that of the paper
passing portion, and the temperature rinsing speed of the paper
non-passing portion due to energization becomes slower than that of
the paper passing portion. Therefore, even in the case where the
temperature of the paper passing portion is risen to be the
overheated state due to energization, the temperature of the paper
non-passing portion shows a lower value than the paper passing
portion, and thereby the overheat preventing element arranged in
the vicinity of the paper non-passing portion is incapable of
indirectly detecting the overheated state of the paper passing
portion accurately from the temperature change in the paper
non-passing portion due to energization. Furthermore, in the
configuration where the paper passing portion and the paper
non-passing portion are electrically connected in series, when the
power density of the paper passing portion and the paper
non-passing portion are set to be the same, the power of the paper
non-passing portion is smaller than that of the paper passing
portion, and thereby the overheat preventing element arranged in
the vicinity of the paper non-passing portion is incapable of
indirectly detecting the overheated state of the paper passing
portion accurately from the temperature change in the paper
non-passing portion due to energization.
[0016] Moreover, the configuration in which the paper passing
portion and the paper non-passing portion are electrically
connected in series is susceptible to a disturbance factor such as
variation in applied voltage to the respective portions, and thus
the temperature change in the respective portions is not the same,
thus it is impossible to indirectly detect the overheated state of
the paper passing portion accurately from the temperature change in
the paper non-passing portion due to energization.
SUMMARY OF THE INVENTION
[0017] Hence, an object of the invention is to provide a fixing
device of belt fixing type configured to heat a fixing belt by
using heat of a resistance heat generating element that generates
heat due to being energized, in which temperature abnormality under
which the resistance heat generating element becomes an overheated
state is able to be detected by an overheat preventing element
accurately in a state where an erroneous operation is prevented,
the resistance heat generating element becoming the overheated
state and resulting in smoke generation or burnout is prevented,
and high safety is able to be secured, and to provide an image
forming apparatus including the fixing device.
[0018] The invention provides a fixing device comprising:
[0019] a first fixing member;
[0020] a heating member;
[0021] a fixing belt that forms an endless-shaped belt member
supported around the first fixing member and the heating member
with tension to be rotatable, and comes into contact with the
heating member to be heated; and
[0022] a second fixing member that forms a fixing nip region
together with the fixing belt, the fixing device fixing a toner
image borne on a recording medium onto the recording medium in the
fixing nip region under application of heat and pressure,
[0023] the heating member including: [0024] a curved heat radiating
member having an outer circumferential surface in contact with the
fixing belt; and [0025] a heat generating member having a heat
generating layer composed of a resistance heat generating element
that generates heat due to being energized and arranged to be in
contact with an inside surface of the heat radiating member,
[0026] the resistance heat generating element including: [0027] a
paper passing region heating section forming a heat generating
source part for heating a paper passing region of the fixing belt
where the recording medium contacts and passes in the fixing nip
region; and [0028] a detecting section that is provided to
correspond to a paper non-contacting region of the recording medium
of the fixing belt and connected electrically in parallel with the
paper passing region heating section, and
[0029] the fixing device further comprising an overheat preventing
element that is provided in a vicinity of the detecting section and
suppresses energization to the resistance heat generating element
when temperature of the detecting section reaches a predetermined
value.
[0030] According to the invention, in the fixing device, a heating
member that heats a fixing belt includes a curved heat radiating
member having an outer circumferential surface in contact with the
fixing belt, and a heat generating member arranged to be in contact
with an inside surface of the heat radiating member. The heat
generating member has a heat generating layer composed of a
resistance heat generating element that generates heat due to being
energized. Then the resistance heat generating element includes a
paper passing region heating section forming a heat generating
source part for heating a paper passing region of the fixing belt
and a detecting section that is provided to correspond to a paper
non-contacting region of the recording medium of the fixing belt
and connected electrically in parallel with the paper passing
region heating section. Moreover, in a vicinity of the detecting
section of the resistance heat generating element, an overheat
preventing element that suppresses energization to the resistance
heat generating element when temperature of the detecting section
reaches a predetermined value, is provided.
[0031] In the fixing device, since it is configured that
energization to the resistance heat generating element is
controlled by an overheat preventing element provided in the
vicinity of the detecting section arranged on an end portion of the
axial direction of the heat generating member corresponding to the
non-contacting region of the recording medium of the fixing belt,
irrespective of the size of the recording medium supplied to the
fixing nip region, it is possible to indirectly detect an
overheated state of the paper passing region from the temperature
change in the detecting section corresponding to the paper
non-passing region of the fixing belt that the recording medium
does not contact all the time, and thereby an erroneous operation
of the overheat preventing element is able to be prevented.
[0032] Further, since the paper passing region heating section and
the detecting section are electrically connected in parallel, the
resistance heat generating element that generates heat due to being
energized is prevented from being subjected to a disturbance factor
such as variation in applied voltage to the paper passing region
heating section and the detecting section. Therefore, when the
resistance heat generating element is energized, the temperature
changes in the paper passing region and the detecting section are
the same, and the overheated state of the paper passing region
heating section is able to be indirectly detected accurately from
the temperature change in the detecting section due to
energization. Accordingly, it is possible to prevent that the paper
passing region heating section of the resistance heat generating
element becomes an overheated state and results in smoke generation
or burnout, and high safety is able to be secured.
[0033] Further, in the invention, it is preferable that the paper
passing region heating section and the detecting section have an
equivalent power density.
[0034] According to the invention, in the resistance heat
generating element that generates heat due to being energized, the
paper passing region heating section and the detecting section have
an equivalent power density. Whereby, when the resistance heat
generating element is energized, the temperature changes in the
paper passing region heating section and the detecting section are
the same, and the overheated state of the paper passing region
heating section is able to be indirectly detected accurately from
the temperature change in the detecting section due to
energization.
[0035] Further, in the invention, it is preferable that the paper
passing region heating section and the detecting section have an
equivalent temperature rising speed in generating heat due to being
energized.
[0036] According to the invention, in the resistance heat
generating element that generates heat due to being energized, the
paper passing region heating section and the detecting section have
an equivalent temperature rising speed in generating heat due to
being energized. Whereby, when the resistance heat generating
element is energized, the temperature changes in the paper passing
region heating section and the detecting section are the same, and
the overheated state of the paper passing region heating section is
able to be indirectly detected accurately from the temperature
change in the detecting section due to energization.
[0037] Further, in the invention, it is preferable that the paper
passing region heating section and the detecting section have an
equivalent specific heat capacity.
[0038] According to the invention, in the resistance heat
generating element that generates heat due to being energized, the
paper passing region heating section and the detecting section have
an equivalent specific heat capacity. Whereby, when the resistance
heat generating element is energized, the temperature changes in
the paper passing region heating section and the detecting section
are the same, and the overheated state of the paper passing region
heating section is able to be indirectly detected accurately from
the temperature change in the detecting section due to
energization.
[0039] Further, in the invention, it is preferable that the
resistance heat generating element is configured to form a surface
of a fixed shape as a whole.
[0040] According to the invention, the resistance heat generating
element is configured to form a surface of a fixed shape as a
whole. Whereby, efficiency of heat transfer in transmitting the
heat of the resistance heat generating element generated due to
energization to the heat radiating member, is able to be
improved.
[0041] Further, in the invention, it is preferable that the
resistance heating element is a ceramic heating element.
[0042] According to the invention, with this configuration, the
resistance heating element is a ceramic heating element. The
ceramic heating element is a heating element that can realize high
power density. Therefore, the heat generating member including the
ceramic heating element has high heating capability with respect to
the heat radiating member.
[0043] Further, in the invention, it is preferable that the
resistance heating element has a positive resistance-temperature
property in which, as temperature rises, electrical resistance
increases.
[0044] According to the invention, the resistance heat generating
element has a positive resistance-temperature property. In the
resistance heat generating element having the positive
resistance-temperature property, electrical resistance increases as
temperature rises. In such a resistance heat generating element
having the positive resistance-temperature property, when the
temperature thereof becomes a predetermined temperature or more,
the electrical resistance sharply increases and the current value
becomes small, thereby it is prevented to be the overheated state.
Moreover, in the resistance heat generating element having the
positive resistance-temperature property, since the current value
becomes small as the temperature rises, amount of power consumption
is able to be reduced and the energy saving is able to be realized.
Moreover, since the resistance heat generating element has the
paper passing region heating section and the detecting section,
even though the resistance heat generating element is the heat
generating element having the positive resistance-temperature
property, it is possible to indirectly detect the overheated state
of the paper passing region heating section accurately from the
temperature change in the detecting section due to
energization.
[0045] Further, in the invention, it is preferable that the
resistance heating element has a negative resistance-temperature
property in which, as temperature rises, electrical resistance
decreases.
[0046] According to the invention, the resistance heat generating
element has a negative resistance-temperature property. In the
resistance heat generating element having the negative
resistance-temperature property, electrical resistance decreases as
temperature rises. Here, since the resistance heat generating
element has the paper passing region heating section and the
detecting section, even in the case where the resistance heat
generating element is the heat generating element having the
negative resistance-temperature property, it is possible to
indirectly detect the overheated state of the paper passing region
heating section accurately from the temperature change in the
detecting section due to energization.
[0047] Further, in the invention, it is preferable that the
resistance heating element has a positive resistance-temperature
property and a negative resistance-temperature property.
[0048] According to the invention, the resistance heat generating
element has a positive resistance-temperature property and a
negative resistance-temperature property. Here, since the
resistance heat generating element has the paper passing region
heating section and the detecting section, even in the case where
the resistance heat generating element is the heat generating
element having the positive resistance-temperature property and the
negative resistance-temperature property, it is possible to
indirectly detect the overheated state of the paper passing region
heating section accurately from the temperature change in the
detecting section due to energization.
[0049] Further, in the invention, it is preferable that the heat
generating member has a heat generating layer composed of a
plurality of the resistance heat generating elements, and is
configured such that a heat generating part that generates heat due
to being energized is divided into more than one,
[0050] each of the plurality of resistance heat generating elements
has the paper passing region heating section and the detecting
section.
[0051] According to the invention, the heat generating member is
configured to have a heat generating layer composed of the
plurality of resistance heat generating elements, and the heat
generating part thereof which generates heat due to being energized
is divided into more than one. Whereby, on/off of energization is
switched for the respective resistance heat generating elements
that correspond to the respective divisions of the heat generating
part, and it is possible to adjust the temperature distribution on
the surface of the heat radiating member in contact with the fixing
belt to be desired temperature distribution. For example, in such
as a case where a toner image is fixed by supplying recording
medium of a different dimension, width, or thickness to the fixing
nip region, by switching on/off of energization so that only the
resistance heat generating element corresponding to a desired
specific region on the surface of the heat radiating member
generates heat, in accordance with the different size (dimension,
width, or thickness) of the recording medium, the surface of the
heat radiating member is able to have the desired temperature
distribution. Whereby, the regional abnormal temperature rise of
the resistance heat generating element corresponding to a
non-contacting part of the recording medium on the surface of the
fixing belt is able to be suppressed.
[0052] Further, each of the plurality of resistance heat generating
elements has the paper passing region heating section and the
detecting section. Whereby, the overheated state of the paper
passing region heating section is able to be indirectly detected
accurately from the temperature change in the detecting section due
to energization, for the respective resistance heat generating
elements that correspond to the respective divisions of the heat
generating part. Accordingly, it is possible to prevent the paper
passing region of each of the resistance heat generating elements
becomes overheated state and results in smoke generating or
burnout, and high safety is able to be secured.
[0053] Further, in the invention, it is preferable that the second
fixing member includes a pressure belt that is an endless-shape
belt member supported around a pressure member and a supporting
member with tension so as to be rotatable, and
[0054] the pressure member is provided to face the first fixing
member with the fixing belt and the pressure belt interposed
therebetween.
[0055] According to the invention, the second fixing member
includes a pressure belt that is an endless-shape belt member
supported around a pressure member and a supporting member with
tension so as to be rotatable. Then the pressure member is provided
to face the first fixing member with the fixing belt and the
pressure belt interposed therebetween, and a fixing nip region is
formed at a part where the fixing belt contacts the pressure belt.
Thereby, a wide fixing nip region is able to be obtained without
enlarging an apparatus, and fixing failure is able to be
suppressed.
[0056] Further, the invention provides a fixing device of two-stage
fixing type, comprising:
[0057] a first fixing section that performs primary fixing of a
toner image borne on a recording medium to be conveyed onto the
recording medium under application of heat and pressure; and
[0058] a second fixing section that is arranged on a downstream
side of a conveyance direction of the recording medium with respect
to the first fixing section, and performs secondary fixing of the
toner image after the primary fixing onto the recording medium
under application of heat and pressure,
[0059] the first fixing section and the second fixing section being
the fixing device mentioned above.
[0060] According to the invention, a fixing device of two-stage
fixing type comprises a first fixing section that performs primary
fixing of a toner image borne on recording medium to be conveyed
onto the recording medium under application of heat and pressure,
and a second fixing section that is arranged on a downstream side
of a conveyance direction of the recording medium with respect to
the first fixing section, and performs secondary fixing of the
toner image after the primary fixing onto the recording medium
under application of heat and pressure. Then the first fixing
section and the second fixing section are the fixing device
mentioned above provided with the resistance heat generating
element in which the paper passing region heating section and the
detecting section are electrically connected in parallel. In the
fixing device of two-stage fixing type thus configured, when the
respective resistance heat generating elements provided in the
first fixing section and the second fixing section are energized,
temperature changes in the paper passing region heating section and
the detecting section of the respective resistance heat generating
elements are the same. Therefore, in each resistance heat
generating element that is provided in the first fixing section and
the second fixing section, the overheated state of the paper
passing region heating section is able to be indirectly detected
accurately from the temperature change in the detecting section due
to energization.
[0061] Accordingly, it is possible to prevent the paper passing
region heating section of the respective resistance heat generating
elements provided in the first fixing section and the second fixing
section from being overheated and generating smoke or burning out,
and to secure high safety.
[0062] Further, the invention provides a fixing device of two-stage
fixing type, comprising:
[0063] a first fixing section that performs primary fixing of a
toner image borne on a recording medium to be conveyed onto the
recording medium under application of heat and pressure; and
[0064] a second fixing section that performs secondary fixing of
the toner image after the primary fixing onto the recording medium
under application of heat and pressure, the second fixing section
being configured by a pair of heating and pressure rollers that are
provided with a heating section in an interior thereof, and are in
pressure-contact with each other, and being arranged on a
downstream side of a conveyance direction of the recording medium
with respect to the first fixing section, and
[0065] the first fixing section being the fixing device mentioned
above.
[0066] According to the invention, a fixing device of two-stage
fixing type comprises a first fixing section that performs fixing
of a toner image borne on recording medium to be conveyed onto the
recording medium under application of heat and pressure, a second
fixing section that performs secondary fixing of the toner image
after the primary fixing onto the recording medium under
application of heat and pressure, the second fixing section being
configured by a pair of heating and pressure roller that are
provided with a heating section in an interior thereof, and are in
pressure-contact with each other, and being arranged on a
downstream side of a conveyance direction of the recording medium
with respect to the first fixing section. Then the first fixing
section is the fixing device provided with the resistance heat
generating element in which the paper passing region heating
section and the detecting section are electrically connected in
parallel. In the fixing device of two-stage fixing type thus
configured, when the resistance heat generating element provided in
the first fixing section is energized, temperature changes in the
paper passing region heating section and the detecting section of
the resistance heat generating element are the same.
[0067] Therefore, in the resistance heat generating element
provided in the first fixing section, the overheated state of the
paper passing region heating section is able to be indirectly
detected accurately from the temperature change in the detecting
section due to energization.
[0068] Accordingly, it is possible to prevent the paper passing
region heating section of the resistance heat generating element
provided in the first fixing section becomes an overheated state
and results in smoke generation or burnout, and high safety is able
to be secured.
[0069] Further, the invention provides an image forming apparatus
including the fixing device mentioned above.
[0070] According to the invention, the image forming apparatus
includes the fixing device capable of preventing the paper passing
region heating section of the resistance heat generating element
from becoming an overheated state and resulting in smoke generation
or burnout, and securing high safety. Therefore, the image forming
apparatus is capable of forming an image in a state where the high
safety is secured over a long term.
BRIEF DESCRIPTION OF DRAWINGS
[0071] Other and further objects, features, and advantages of the
invention will be more explicit from the following detailed
description taken with reference to the drawings wherein:
[0072] FIG. 1 is a view showing a structure of an image forming
apparatus according to an embodiment of the invention;
[0073] FIG. 2 is a view showing a structure of a fixing device
according to a first embodiment of the invention;
[0074] FIG. 3 is a view showing a configuration of a heating member
provided in the fixing device;
[0075] FIG. 4 is a view showing a configuration of a resistance
heat generating element;
[0076] FIGS. 5A to 5E are views showing an arranged position of an
overheat preventing element in a vicinity of a detecting section of
the resistance heat generating element;
[0077] FIG. 6 is a view showing a configuration of a heat
generating layer formed by a plurality of resistance heat
generating elements;
[0078] FIGS. 7A and 7B are views showing a divided state of a paper
passing region heating section of the resistance heat generating
element in the heat generating layer;
[0079] FIGS. 8A to 8D are views showing another example of a
divided state of the paper passing region heating section;
[0080] FIGS. 9A and 9B are views showing a divided state of a paper
passing region heating section in a heat generating layer having a
layered structure in which a plurality of resistance heat
generating elements are layered;
[0081] FIGS. 10A and 10B are views showing a configuration of a
heating member having a structure in which a plurality of
semiconductor ceramic elements are held by a heat radiating
member;
[0082] FIG. 11 is a view showing a configuration of a fixing device
according to a second embodiment of the invention;
[0083] FIG. 12 is a view showing a configuration of a fixing device
according to a third embodiment of the invention; and
[0084] FIG. 13 is a view showing a configuration of a fixing device
according to a fourth embodiment of the invention.
DETAILED DESCRIPTION
[0085] Now referring to the drawings, preferred embodiments of the
invention are described below.
[0086] FIG. 1 is a view showing the structure of an image forming
apparatus 100 according to an embodiment of the invention. The
image forming apparatus 100 is an apparatus that forms a color or
monochrome image on a recording paper sheet based on image data
read from a document or on image data transmitted through a network
and the like. The image forming apparatus 100 includes an exposure
unit 10, photoreceptor drums 101 (101a to 101d), developing devices
102 (102a to 102d), charging rollers 103 (103a to 103d), cleaning
units 104 (104a to 104d), an intermediate transfer belt 11, primary
transfer rollers 13 (13a to 13d), a secondary transfer roller 14, a
fixing device 15, paper conveyance paths P1, P2, and P3, a paper
feeding cassette 16, a manual paper feeding tray 17, and a catch
tray 18.
[0087] The image forming apparatus 100 performs image formation by
using image data corresponding to each of the four colors of black
(K), as well as cyan (C), magenta (M), and yellow (Y), which are
the three primary subtractive colors obtained by separating colors
of a color image, in image forming sections Pa to Pd corresponding
to the respective colors. The respective image forming sections Pa
to Pd are similar to one another in configuration, and for example,
the image forming section Pa for black (K) is constituted by the
photoreceptor drum 101a, the developing device 102a, the charging
roller 103a, the primary transfer roller 13a, the cleaning unit
104a, and the like. The image forming sections Pa to Pd are
arranged in alignment along a direction in which the intermediate
transfer belt 11 moves (sub-scanning direction).
[0088] The charging rollers 103 are contact-type charging devices
for charging surfaces of the photoreceptor drums 101 uniformly to a
predetermined potential. Instead of the charging rollers 103,
contact-type charging devices using a charging brush, or
noncontact-type charging devices using a charging wire is also
usable.
[0089] The exposure unit 10 includes a semiconductor laser (not
shown), a polygon mirror 4, a first reflection mirror, a second
reflection mirror 8, and the like, and irradiates each of the
photoreceptor drums 101a to 101d with each light beam such as a
laser beam modulated according to image data of the respective
colors of black (K), cyan (C), magenta (M), and yellow (Y). Each of
the photoreceptor drums 101a to 101d forms thereon an electrostatic
latent image corresponding to the image data of the respective
colors of black (K), cyan (C), magenta (M), and yellow (Y).
[0090] The developing devices 102 supply toner as developer to the
surfaces of the photoreceptor drums 101 on which the electrostatic
latent images are formed, to develop the electrostatic latent
images to a toner image. The respective developing devices 102a to
102d contain toner of the respective colors of black (K), cyan (C),
magenta (M), and yellow (Y), and visualize the electrostatic latent
images of the respective colors formed on the respective
photoreceptor drums 101a to 101d into toner images of the
respective colors. The cleaning units 104 remove and collect
residual toner on the surfaces of the photoreceptor drums 101 after
development and image transfer.
[0091] The intermediate transfer belt 11 provided above the
photoreceptor drums 101 is supported around a driving roller 11a
and a driven roller 11b with tension, and forms a loop-shaped
moving path. An outer circumferential surface of the intermediate
transfer belt 11 faces the photoreceptor drum 101d, the
photoreceptor drum 101c, the photoreceptor drum 101b and the
photoreceptor drum 101a in this order. The primary transfer rollers
13a to 13d are disposed at positions facing the respective
photoreceptor drums 101a to 101d with the intermediate transfer
belt 11 interposed therebetween. The respective positions at which
the intermediate transfer belt 11 faces the photoreceptor drums
101a to 101d are primary transfer positions. In addition, the
intermediate transfer belt 11 is formed of a film having thickness
of 100 to 150 .mu.m.
[0092] A primary transfer bias voltage having an opposite polarity
to the polarity of the toner is applied under constant voltage
control to the primary transfer rollers 13a to 13d in order to
transfer the toner images borne on the surfaces of the
photoreceptor drums 101a to 101d onto the intermediate transfer
belt 11. Thus, the toner images of the respective colors formed on
the photoreceptor drums 101a to 101d are transferred and overlapped
onto the outer circumferential surface of the intermediate transfer
belt 11 on top of each other to form a full-color toner image on
the outer circumferential surface of the intermediate transfer belt
11.
[0093] Here, when image data for only a part of the colors of
yellow (Y), magenta (M), cyan (C) and black (B) is inputted,
electrostatic latent images and toner images are formed at only a
part of the photoreceptor drums 101 corresponding to the colors of
the inputted image data among the four photoreceptor drums 101a to
101d. For example, during monochrome image formation, an
electrostatic latent image and a toner image are formed only at the
photoreceptor drum 101a corresponding to black color, and only a
black toner image is transferred onto the outer circumferential
surface of the intermediate transfer belt 11.
[0094] The respective primary transfer rollers 13a to 13d have a
structure comprising a shaft having a diameter of 8 to 10 mm, made
of a metal such as stainless steel and serving as a substrate, and
a conductive elastic material (for example, EPDM or urethane foam)
with which a surface of the shaft is coated, and uniformly apply a
high voltage to the intermediate transfer belt 11 by the conductive
elastic material.
[0095] The toner image transferred onto the outer circumferential
surface of the intermediate transfer belt 11 at each of the primary
transfer positions is conveyed to a secondary transfer position,
which is a position facing the secondary transfer roller 14, by the
rotation of the intermediate transfer belt 11. The secondary
transfer roller 14 is brought into pressure-contact with, at a
predetermined nip pressure, the outer circumferential surface of
the intermediate transfer belt 11 whose inner circumferential
surface is in contact with a circumferential surface of the driving
roller 11a during image formation. While a recording paper sheet
fed from the paper feeding cassette 16 or the manual paper feeding
tray 17 passes between the secondary transfer roller 14 and the
intermediate transfer belt 11, a high voltage with the opposite
polarity to the charging polarity of the toner is applied to the
secondary transfer roller 14. Thus, the toner image is transferred
from the outer circumferential surface of the intermediate transfer
belt 11 to the surface of the recording paper sheet.
[0096] Note that, of the toner attached from the photoreceptor
drums 101 to the intermediate transfer belt 11, toner that has not
been transferred onto the recording paper sheet and remains on the
intermediate transfer belt 11 is collected by a transfer cleaning
unit 12 in order to prevent color mixture in the following
process.
[0097] The recording paper sheet to which the toner image is
transferred is guided to a fixing device 15 described below
according to an embodiment of the invention, passes through the
fixing nip region, and is subjected to heat and pressure. Thus, the
toner image is solidly fixed onto the surface of the recording
paper sheet. The recording paper sheet onto which the toner image
is fixed is discharged onto the sheet discharge tray 18 by the
sheet discharge roller 18a.
[0098] Moreover, the image forming apparatus 100 is provided with
the paper conveyance path P1 extending in the substantially
vertical direction, for feeding a recording paper sheet contained
in the paper feeding cassette 16 through a region between the
secondary transfer roller 14 and the intermediate transfer belt 11,
and by way of the fixing device 15, to the catch tray 18. The paper
conveyance path P1 is provided with a pickup roller 16a for picking
up recording paper sheets in the paper feeding cassette 16 in the
paper conveyance path P1 sheet by sheet, conveying rollers 16b for
conveying the fed recording paper sheet upward, registration
rollers 19 for guiding the conveyed recording paper sheet between
the secondary transfer roller 14 and the intermediate transfer belt
11 at a predetermined timing, and the paper discharge rollers 18a
for discharging the recording paper sheet onto the catch tray
18.
[0099] Moreover, inside the image forming apparatus 100, the paper
conveyance path P2 on which a pickup roller 17a and conveying
rollers 16b are disposed is formed between the manual paper feeding
tray 17 and the registration rollers 19. In addition, the paper
conveyance path P3 is formed between the paper discharge rollers
18a and the upstream side of the registration rollers 19 in the
paper conveyance path P1.
[0100] The paper discharge rollers 18a freely rotate in both
forward and reverse directions, and are driven in the forward
direction to discharge a recording paper sheet onto the catch tray
18 during single-sided image formation in which images are formed
on one side of the recording paper sheets, and during second side
image formation of double-sided image formation in which images are
formed on both sides of the recording paper sheet. On the other
hand, during first side image formation of double-sided image
formation, the paper discharge rollers 18a are driven in the
forward direction until a tail edge of the sheet passes through the
fixing device 15, and are then driven in the reverse direction to
bring the recording paper sheet into the paper conveyance path P3
in a state where the tail edge of the recording paper sheet is
held. Thus, the recording paper sheet on which an image has been
formed only on one side during double-sided image formation is
brought into the paper conveyance path P1 in a state where the
recording paper sheet is turned over and upside down.
[0101] The registration rollers 19 bring the recording paper sheet
that has been fed from the paper feeding cassette 16 or the manual
paper feeding tray 17, or has been conveyed through the paper
conveyance path P3 between the secondary transfer roller 14 and the
intermediate transfer belt 11 at a timing synchronized with the
rotation of the intermediate transfer belt 11. Thus, the rotation
of the registration rollers 19 is stopped when the operation of the
photoreceptor drums 101 or the intermediate transfer belt 11 is
started, and the movement of the recording paper sheet that has
been fed or conveyed prior to the rotation of the intermediate
transfer belt 11 is stopped in the paper conveyance path P1 in a
state where a leading edge thereof abuts against the registration
rollers 19. Then, the rotation of the registration rollers 19 is
started at a timing when the leading edge of the recording paper
sheet faces a leading edge of a toner image formed on the
intermediate transfer belt 11 at a position where the secondary
transfer roller 14 is brought into pressure-contact with the
intermediate transfer belt 11.
[0102] Note that, during full-color image formation in which image
formation is performed by all of the image forming sections Pa to
Pd, all of the primary transfer rollers 13a to 13d bring the
intermediate transfer belt 11 into pressure-contact with the
photoreceptor drums 101a to 101d. On the other hand, during
monochrome image formation in which image formation is performed
only by the image forming section Pa, only the primary transfer
roller 13a brings the intermediate transfer belt 11 into
pressure-contact with the photoreceptor drum 101a.
[0103] FIG. 2 is a view showing the structure of the fixing device
15 according to a first embodiment of the invention. The fixing
device 15 includes a fixing roller 15a serving as a first fixing
member, a pressure roller 15b serving as a second fixing member, a
fixing belt 25 serving as an endless-shaped belt member, and a
heating member 21. In the fixing device 15, the fixing belt 25 is
supported around the fixing roller 15a and the heating member 21
with tension, and the pressure roller 15b is disposed so as to face
the fixing roller 15a, with the fixing belt 25 interposed
therebetween. Moreover, the fixing roller 15a and the heating
member 21 are arranged substantially in parallel with each other in
an axial direction of the fixing roller 15a. With this arrangement,
the fixing belt 25 supported around the fixing roller 15a and the
heating member 21 with tension can be prevented from running
windingly during its sliding movement, wherefore the durability of
the fixing belt 25 can be maintained at a high level.
[0104] The fixing device 15 is a fixing device of belt fixing type
in which the heating member 21 comes into contact with the fixing
belt 25 to heat the fixing belt 25, and when the recording paper
sheet 32 serving as a recording medium passes through the fixing
nip region 15c defined by the fixing belt 25 and the pressure
roller 15b at predetermined fixing speed and copy speed, fixes the
unfixed toner images 31 borne on the recording paper sheet 32 under
application of heat and pressure. The fixing device 15 of belt
fixing type is configured such that the fixing belt 25 having a
small heat capacity is heated by the heating member 21 having the
high-power-density heat generating layer 212. Therefore, a warm-up
time is short, and an increase in power consumption is suppressed,
thereby achieving power savings.
[0105] Note that the unfixed toner image 31 is formed of, for
example, a developer (toner) such as a non-magnetic one-component
type developer (non-magnetic toner), a non-magnetic two-component
type developer (non-magnetic toner and carrier), or a magnetic
developer (magnetic toner). Moreover, the "fixing speed"
corresponds to a so-called process speed, and the "copying speed"
corresponds to the number of copies obtained per minute. Further,
when the recording paper sheet 32 passes through the fixing nip
region 15c, the fixing belt 25 abuts against that surface of the
recording paper sheet 32 which is opposite from the toner
image-bearing surface thereof.
[0106] The fixing roller 15a is brought into pressure-contact with
the pressure roller 15b with the fixing belt 25 interposed
therebetween to thereby form the fixing nip region 15c, and at the
same time, is rotated in a rotation direction A around a rotation
axis by a not-shown driving motor (driving section) to thereby
cause the fixing belt 25 to run. The fixing roller 15a has a
diameter of 30 mm and has a two-layered structure consisting of a
core metal and an elastic layer, which are formed in this order
from inside. For the core metal, for example, a metal such as iron,
stainless steel, aluminum, and copper, an alloy thereof, or the
like are used. Moreover, for the elastic layer, a rubber material
having heat resistance such as silicone rubber and fluorine rubber
is suitable. Note that, in this embodiment, a force when the fixing
roller 15a is brought into pressure-contact with the pressure
roller 15b with the fixing belt 25 interposed therebetween is about
216 N.
[0107] The pressure roller 15b is provided to be opposite and in
pressure-contact with the fixing roller 15a with the fixing belt 25
interposed between. The pressure roller 15b is freely rotatable
around its rotation axis. The pressure roller 15b is rotated in a
rotation direction B by rotation of the fixing roller 15a. The
pressure roller 15b has a three-layered structure consisting of a
core metal, an elastic layer, and a release layer, which are formed
in this order from inside. For the core metal, for example, a
metal, such as iron, stainless steel, aluminum, or copper, or an
alloy thereof is used. For the elastic layer, a heat resistant
rubber material such as silicone rubber or fluorine rubber is
suitable. For the release layer, fluorine resin such as PFA (a
copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) or
PTFE (polytetrafluoroethylene) is suitable. For the pressure roller
15b, for example, a roller may be used in which the diameter of the
roller is 30 mm, an iron (STKM) pipe having a diameter of 24 mm
(thickness 2 mm) is used for the core metal, solid silicon rubber
having a thickness of 3 mm is used for the elastic layer, and a PFA
tube having a thickness of 30 .mu.m is used for the release
layer.
[0108] The pressure roller 15b is provided with a heater lamp 26
(for example, rated power 400 W) in an interior thereof to heat the
pressure roller 15b. A control circuit (not shown) causes power to
be supplied (energized) from a power supply circuit (not shown) to
the heater lamp 26, the heater lamp 26 emits light, and infrared
rays are radiated from the heater lamp 26. Thus, the inner
circumferential surface of the pressure roller 15b absorbs the
infrared rays and is heated, such that the entire pressure roller
15b is heated. Although the above-described heater lamp 26 heats
the pressure roller 15b from the inner surface, the pressure roller
15b may be heated by a roller for outer circumference heating, from
a surface thereof.
[0109] The fixing belt 25 is heated to a predetermined temperature
by the heating member 21 and heats the recording paper sheet 32
having the unfixed toner image 31 formed thereon that passes
through the fixing nip region 15c. The fixing belt 25 is an
endless-shaped belt and is supported around the heating member 21
and the fixing roller 15a and wound up by the fixing roller 15a
with a predetermined angle. During rotation of the fixing roller
15a, the fixing belt 25 is rotated in the rotation direction A by
rotation of the fixing roller 15a. The fixing belt 25 has a
three-layered structure consisting of a substrate having a hollow
cylindrical shape made of a heat resistant resin such as polyimide
or a metal material such as stainless steel and nickel, an elastic
layer formed on a surface of the substrate, made of an elastomer
material (for example, silicone rubber) having excellent heat
resistance and elastic property, and a release layer formed on a
surface of the elastic layer, made of a synthetic resin material
(for example, a fluorine resin such as PFA or PTFE) having
excellent heat resistance and releasing property. Moreover, a
fluorine resin may be added into polyimide constituting the
substrate. This makes it possible to reduce a slide load with the
heating member 50.
[0110] The heating member 21 is a member that comes into contact
with the fixing belt 25 to heat the fixing belt 25 to a
predetermined temperature. In the fixing device 15, a heat
generating element-side thermistor 24a and a pressure roller-side
thermistor 24b serving as a temperature detecting section are
respectively provided on the circumferential surface of the fixing
belt 25 in contact with the heating member 21 and on the
circumferential surface of the pressure roller 15b to detect
surface temperature.
[0111] FIG. 3 is a view showing a configuration of the heating
member 21 provided in the fixing device 15. The heating member 21
has a semicircular shape and includes a heat radiating member 210,
a heat generating member 211 and an inside securing member 218.
[0112] The heat radiating member 210 is a member which extends in a
width direction of the fixing belt 25 (an axial direction of the
fixing roller 15a) and has a curved shape along a surface of the
fixing belt 25, and is arranged to contact the fixing belt 25 on
the outer circumferential surface thereof so as to transmit heat
generated from the heat generating member 211 to the fixing belt
25. Although a material that constitutes the heat radiating member
210 is not particularly limited, a metal material having high
thermal conductivity is preferable, and as the metal material,
iron, aluminum, copper or the like is able to be included, however,
stainless steel is also usable. Then, in the heat radiating member
210, a coat layer 214 is formed on the outer circumferential
surface thereof in contact with the fixing belt 25.
[0113] The coat layer 214 should be formed by a material having
thermal conductivity for conducting heat generated from the heat
generating member 211 to the fixing belt 25, and capable of
reducing the frictional force with the fixing belt 25. By forming
such a coat layer 214, heat is conducted to the fixing belt 25 as
well as wear of the fixing belt 25 that slides in contact with the
heat radiating member 210 is prevented so that excellent durability
is able to be secured. Moreover, since the frictional force with
the fixing belt 25 is able to be reduced, load to the fixing roller
15a and the pressure roller 15b which drive the fixing belt 25 is
able to be reduced, and durability of the respective rollers 15a
and 15b is ensured, thus enables driving by a lower torque.
Examples of the material constituting the coat layer 214 include a
fluorine resin such as a PFA or a PTFE. In the embodiment, the coat
layer 214 is a layer formed of a PTFE and having a thickness of 20
.mu.m.
[0114] The inside securing member 218 is a member that holds the
heat generating member 211 by being in line-contact with or in
point-contact with one surface of a thickness direction of the heat
generating member 211 so as to elastically press the heat
generating member 211 toward a direction moving closer to the heat
radiating member 210 and by allowing another surface of the
thickness direction of the heat generating member 211 to be in
surface-contact with the inside surface of the heat radiating
member 210. The inside securing member 218 allows the heat
generating layer 212 composed of the resistance heat generating
element such as a ceramic heat generating element or a metallic
heat generating element to contact an inner surface stably so that
heat generated from the heat generating layer 212 is
heat-transferred effectively to the heat radiating member 210, and
thereby prevents that only the resistance heat generating element
of the heat generating layer 212 is regionally overheated and
breakage thereof is caused.
[0115] In the embodiment, the inside securing member 218 is a
spiral-shaped member formed to be a spiral shape using a wire.
Specifically, a wire formed of stainless steel and having a wire
diameter of 1 mm is formed to be a spiral shape and an outer
diameter of the coil in a stationary placed state is 29.5 mm, and a
space between respective spires is 5 mm. A material constituting
the wire may be, other than stainless steel, for example, copper,
iron, nickel, alloy thereof, or heat resistant resin. In a case
where the inside securing member 218 is formed of the heat
resistant resin, the member is able to be caused to be more
excellent in heat insulation compared with a case of being formed
by metal, and it is possible to increase an effect to suppress heat
loss caused by transmitting heat generated in the heat generating
layer 212 to the inside securing member 218 and dissipated. On the
other hand, in a case where the inside securing member 218 is
formed of metal, the member is able to be caused to be more
excellent in heat resistance and elastic coefficient thereof is
higher compared with a case of being formed by the resin, and it is
possible to increase an effect of elastically pressing the heat
generating member 211 toward the direction moving closer to the
heat radiating member 210 so as to hold stably at a predetermined
position.
[0116] In addition, the wire diameter, the coil outer diameter, the
space of spires, and constituent material of the wire are not
limited to the above-described configuration, and setting may be
performed such that spring elasticity is able to be exerted under
high temperature environment when formed into a spiral shape.
[0117] A fixing method of holding and fixing the heat generating
member 211 using the inside securing member 218 at a predetermined
position which faces the inside surface of the heat radiating
member 210 is as follows. First, another surface of the thickness
direction of the heat generating member 211 is arranged to face the
inside surface of the heat radiating member 210. Next, the inside
securing member 218 formed to be a spiral shape is fixed so that,
of an outer circumferential part of each of the spires of the
spiral shaped part which lies outwardly in a radial direction
thereof, an entire part facing a surface of the thickness direction
of the heat generating member 211 is to be in line-contact with an
entire region across a circumferential direction (short-side
direction) of the heat generating member 211. At this time, in the
inside securing member 218 formed to be a spiral shape, force to
restore acts by the elasticity generated by the change of the coil
outer diameter in the spiral shaped part, and the restoring force
to restore acts as force to elastically press the heat generating
member 211 toward the direction moving closer to the heat radiating
member 210. In this manner, since the restoring force of the inside
securing member 218 acts to hold the heat generating member 211 on
the inside surface of the heat radiating member 210, the heat
generating member 211 is held in a state where another surface of
the thickness direction thereof is in surface-contact with the
inside surface of the heat radiating member 210.
[0118] Since the heat generating member 211 is elastically pressed
and held toward the direction moving closer to the heat radiating
member 210 by the restoring force of the inside securing member
218, even though the heat radiating member 210 and the heat
generating member 211 expand and contract by heating, or the inside
securing member 218 itself expands and contracts by heat, the
spiral shaped part of the inside securing member 218 shifts in
accordance with the expansion and contraction, and thereby the heat
generating member 211 is able to be stably held at a predetermined
position on the inside surface of the heat radiating member 210.
Moreover, by changing the space and the arranged position of each
of the spires in the spiral shaped part of the inside securing
member 218, pressing force distribution of the heat generating
member 211 against the inside surface of the heat radiating member
210 is able to be changed.
[0119] As above, the heating member 21 in which the inside securing
member 218 is in line-contact with a surface of the thickness
direction of the heat generating member 211 to elastically press
the heat generating member 211 toward the direction moving closer
to the heat radiating member 210, and the heat generating member
211 is held so that another surface of the thickness direction
thereof is in surface-contact with the inside surface of the heat
radiating member 210.
[0120] Note that, in the inside securing member 218, other than
forming into a spiral shape by using a wire whose cross-section is
a circular shape, an extra fine plate-like member whose
cross-section is an elliptical shape or a polygonal shape may be
used to form a spiral shape. Furthermore, a shape of each of the
spires when viewed from the axial direction in a state where the
inside securing member 218 formed to be a spiral shape is
stationary placed is able to be set to various shapes.
Additionally, in the embodiment, although the inside securing
member 218 formed into a spiral shape is used, it is not limited
thereto, and may be configured by various shapes and material, when
the configuration is such that holding the heat generating member
211 by being in line-contact with or in point-contact with the
surface of the thickness direction of the heat generating member
211 so as to elastically press the heat generating member 211
toward the direction moving closer to the heat radiating member 210
and thereby allows another surface of the thickness direction of
the heat generating member 211 to be in surface-contact with the
inside surface of the heat radiating member 210.
[0121] The heat generating member 211 is held so that the inside
securing member 218 is in line-contact or in point-contact with a
surface of the thickness direction thereof and thereby allows
another surface of the thickness direction thereof to be in
surface-contact with the heat radiating member 210. The heat
generating member 211 has a layered structure in which on the
surface of a second insulating layer 215, a heat generating layer
212, a second good thermal conductor layer 217, a first insulating
layer 213, and a first good thermal conductor layer 216 are layered
in this order, and a surface of a side on which the second
insulating layer 215 is formed is a surface of a side in contact
with the inside securing member 218, and a surface of a side on
which the first good thermal conductor layer 216 is formed is a
surface of a side in contact with the inside surface of the heat
radiating member 210. Then, the heat generating member 211 extends
in the longitudinal direction of the heat radiating member 210
(width direction of the fixing belt 25), and is held by the inside
securing member 218 so as to be in surface-contact with the heat
radiating member 210 along a curved inside surface thereof. Then,
at both end portions in the longitudinal direction of the heat
generating member 211 (longitudinal direction of the heat radiating
member 210), power feeding terminal sections 221 are formed.
[0122] The first insulating layer 213 and the second insulating
layer 215 are layers formed by a material having both the heat
resistance and the electrical insulation properties. As the
material having both the heat resistance and the electrical
insulation properties, although not particularly limited, examples
thereof include a heat resistant polymer material such as a
polyimide resin and ceramics material such as alumina. In the
embodiment, the first insulating layer 213 and the second
insulating layer 215 are layers formed of a polyimide resin and
having a thickness of 30 .mu.m. The first insulating layer 213 is
interposed between the heat generating layer 212 and the heat
radiating member 210 to ensure insulation therebetween, and the
second insulating layer 215 is interposed between the heat
generating layer 212 and the inside securing member 218 to ensure
insulation therebetween. In this manner, since the first insulating
layer 213 and the second insulating layer 215 electrically insulate
the heat generating layer 212 composed of the resistance heat
generating element that generates heat due to being energized, it
is possible obtain the heating member 21 being free from danger.
Furthermore, in the embodiment, although it is configured that two
layers each formed of a polyimide resin and having a thickness of
30 .mu.m are provided as the insulator, in order to improve
electrical insulation property, the thickness may be made thicker
(for example, 100 .mu.m) or the number of layers may be increased.
In addition, the first insulating layer 213 and the second
insulating layer 215 are preferable to have the high thermal
conductivity, and thereby degradation of the heating property of
the heating member 21 is able to be prevented.
[0123] The first good thermal conductor layer 216 that is
interposed between the heat radiating member 210 and the first
insulating layer 216, and the second good thermal conductor layer
217 that is interposed between the heat generating layer 212 and
the first insulating layer 216 are layers formed for improving the
thermal conductivity with which heat generated in the heat
generating layer 212 is conducted to the heat radiating member 210.
As a material constituting the first good thermal conductor layer
216 and the second good thermal conductor layer 217, although not
particularly limited when the material is excellent in thermal
conductivity even under the high temperature environment and hard
to cause a time-dependent change, examples thereof include a heat
resistant silicone grease having heat resistance of 300.degree. C.
or more. Furthermore, in order to further improve the thermal
conductivity, one that powder of gold, silver, copper, platinum,
carbon or graphite is added to the heat resistant silicone grease
may be used, and when the substance is such as rubber, metal which
is rich in elasticity, or the like, to accelerate the thermal
conduction by filling a gap of a contact part, although the
material is not particularly limited, nor the form of solid, liquid
or gas is considered, the one whose heat capacity is small and
thermal conductivity is high is preferable. Moreover, the first
good thermal conductor layer 216 and the second good thermal
conductor layer 217 are preferable to have the higher thermal
conductivity than other that of layers constituting the heat
generating member 211, and thereby degradation of the heating
property of the heating member 21 is able to be prevented.
[0124] When a space is formed between the heat generating layer 212
and the first insulating layer 213, and in a overlapping part on
the surface of the side that contacts the inside surface of the
heat radiating member 210, a layer of air is interposed
therebetween and thereby the thermal conductivity deteriorates.
Therefore, by arranging the first and second good thermal conductor
layers 216 and 217, the layer of air that increases resistance to
heat is removed and thereby the thermal conductivity is able to be
improved. Moreover, when the first good thermal conductor layer 216
is arranged between the heat generating layer 212 and the first
insulating layer 213, and the second good thermal conductor layer
217 is arranged on the surface of the side that contacts the inside
surface of the heat radiating member 210, since heat generated in
the heat generating layer 212 is quickly transmitted to the inside
surface of the heat radiating member 210 through the first and
second good thermal conductor layers 216 and 217, shortening of the
warm-up time or uniformity of the temperature distribution on the
surface of the heat radiating member 210 is able to be ensured in a
short time, and even in the high-speed printing, sufficient amount
of heat is able to be supplied from the heat radiating member 210
to the fixing belt 25.
[0125] Next, description will be given for the heat generating
layer 212 provided in the heat generating member 211. The heat
generating layer 212 is a layer composed of the resistance heat
generating element that generates heat with the Joule heat
generated by applying voltage to the power feeding terminal section
221 to be energized. FIG. 4 is a view showing a configuration of
the resistance heat generating element 301 formed on the heat
generating layer 212. In the heat generating layer 212, one piece
of resistance heat generating element 301 repeats flexions so as to
form a fixed surface as a whole. Whereby, the efficiency of heat
transfer in transmitting heat of the resistance heat generating
element 301 generated due to being energized to the heat radiating
member 210 is able to be improved.
[0126] Examples of the resistance heating element 301 constituting
the heat generating layer 212 include a metal material mainly
containing nickel-chromium alloy, a metal resistor having an
electrically resistive component made of stainless steel, and a
resistant material such as silver-palladium-based material. A
ceramic heating element in which a resistance wire having a width
of about 1 mm is formed on a ceramic substrate having a width of 12
mm by screen printing, a ceramic heating element in which a
plurality of thin-film ceramic sheets are laminated and a fine
resistance wire is formed between the sheets and fired, or a
ceramic heating element in which an inorganic material mainly
containing barium titanate-based semiconductor ceramic is fired may
be used as a resistance heating element 301. A ceramic heating
element is a heating element that can realize high power density.
Thus, the heat generating member 211 that has the heat generating
layer 212 including a ceramic heating element has a high
thermoresponsive rate, thereby reducing the warm-up time, and has
high heating capability with respect to the heat radiating member
210.
[0127] The resistance heat generating element 301 then includes a
paper passing region heating section 301a and a detecting section
301b. The paper passing region heating section 301a of the
resistance heat generating element 301 is formed in a region which
is the heat generating source part for heating the paper passing
region of the fixing belt 25, which is on the surface of the heat
generating layer 212. The detecting section 301b of the resistance
heat generating element 301 is provided on an end portion of the
axial direction (longitudinal direction) of the heat generating
member 211 corresponding to the paper non-contacting region of the
recording paper sheet 32 (region that even the recording paper
sheet 32 of a maximum size does not contact) on the fixing belt 25,
and electrically connected in parallel with the paper passing
region heating section 301a.
[0128] Note that, the paper passing region heating section 301a of
the heat generating layer 212 is formed to have a substantially
equivalent area to a contact area where the heat radiating member
210 contacts the fixing belt 25, and the detecting section 301b of
the heat generating layer 212 is formed to have a substantially
equivalent area to a heat receiving surface of an overheat
preventing element 40.
[0129] Then, in a vicinity of the detecting section 301b of the
resistance heat generating element 301, the overheat preventing
element 40 is provided. The overheat preventing element 40 is one
which suppresses energization to the resistance heat generating
element 301 when the temperature of the detecting section 301b of
the resistance heat generating element 301 reaches a predetermined
value, and for example, a thermostat or a thermal protector. The
overheat preventing element 40 formed of the thermostat or the
thermal protector receives heat energy radiated from the detecting
section 301b on the heat receiving surface and when the temperature
of the detecting section 301b reaches the predetermined value,
bimetal inside thereof acts to open a contact circuit so as to cut
off the energization to the resistance heat generating element
301.
[0130] FIGS. 5A to 5E are views showing an arranged position of the
overheat preventing element 40 in a vicinity of the detecting
section 301b of the resistance heat generating element 301. The
overheat preventing element 40 is provided in the vicinity of the
detecting section 301b so as to detect the temperature change due
to energization in the detecting section 301b of the resistance
heat generating element 301. Here, since the temperature rising
speed, the thermal conductivity or the radiant condition varies
depending on an element such as curvature of the surface (detecting
surface) of a target object arranged opposite to the overheat
preventing element 40, an area, the structure and the material of
the heat receiving surface of the overheat preventing element 40
itself, or the structure and the material of each of layers of the
heat generating member 211, the arranging position of the overheat
preventing element 40 is decided in consideration of these
points.
[0131] The overheat preventing element 40 may be arranged opposite
to the second insulating layer 215 in a contact manner as shown in
FIG. 5A, or in a non-contact manner as shown in FIG. 5B, the second
insulating layer 215 corresponding to a region part of the heat
generating layer 212 in which the detecting section 301b of the
resistance heat generating element 301 is provided, the region part
being an end portion of the axial direction (longitudinal
direction) of the heat radiating member 210 in contact with the
fixing belt 25.
[0132] Furthermore, the overheat preventing element 40 may be
arranged opposite to the heat radiating member 210 in a contact
manner as shown in FIG. 5C, or may be arranged opposite to the heat
generating member 212 in a contact manner, corresponding to a
region part, in which the second insulating layer 215 is not
formed, of the heat generating layer 212 in which the detecting
section 301b of the resistance heat generating element 301 is
provided, the region part being an end portion of the axial
direction (longitudinal direction) of the heat radiating member 210
in non-contact with the fixing belt 25. Moreover, as shown in FIG.
5E, the overheat preventing element 40 may be arranged opposite to
the second insulating layer 215 in a non-contact manner, the second
insulating layer 215 corresponding to a region part of the heat
generating layer 212 in which the detecting section 301b of the
resistance heat generating element 301 is provided, the region part
being an end portion of the axial direction (longitudinal
direction) of the heat radiating member 210 in non-contact with the
fixing belt 25.
[0133] When the heat generating layer 212 generates heat by
applying voltage to the resistance heat generating element 301 from
the power feeding terminal section 221, and the fixing belt 25
coming into contact with the heat radiating member 210 is heated by
using the generated heat, in a case where the control of
energization to the resistance heat generating element 301
constituting the heat generating layer 212 is not able to be
performed because of the failure of the control circuit, an
unexpected control program behavior, or the failure of the
switching element, there is a case where the resistance heat
generating element 301 becomes an overheated state and results in
smoke generation, ignition, or burnout.
[0134] The overheat preventing element 40 detects the temperature
abnormality under which the resistance heat generating element 301
becomes the overheated state, and by suppressing the energization
to the resistance heat generating element 301 based on the
detection result, it is possible to prevent that the resistance
heat generating element 301 results in smoke generation, ignition,
or burnout.
[0135] Additionally, since the resistance heat generating element
301 of high power density has high temperature rising speed due to
energization, in order to prevent the resistance heat generating
element 301 from becoming overheated state, the temperature
abnormality under which the resistance heat generating element 301
becomes the overheated state should be detected further earlier.
Furthermore, unless the temperature abnormality detection is
executed by the overheat preventing element 40 at a place where
temperature rising speed is high or a place where power density is
high in the resistance heat generating element 301, it is
impossible to prevent the resistance heat generating element 301 to
result in smoke generation, ignition or burnout when there is a
part which has greater temperature change than the detected
part.
[0136] In order to detect the temperature abnormality under which
the resistance heat generating element 301 becomes the overheated
state further earlier, the overheat preventing element 40 may be
arranged to be in contact with the fixing belt 25 or the heating
member 21, however, in such a case, there is a possibility that as
well as a failure occurs in a fixed image on the recording paper
sheet 32, the temperature distribution of the surface of the fixing
belt 25 becomes non-uniform. Moreover, when the overheat preventing
element 40 is arranged to be in contact with the fixing belt 25 or
the heating member 21, there is a possibility that detection
sensitivity of the overheat preventing element 40 becomes poor and
thereby the temperature abnormality itself is not possible to be
detected.
[0137] Moreover, in the fixing device 15, a width of a paper
non-passing region on the surface of the fixing belt 25 varies
depending on a size of the recording paper sheet 32 to be supplied
to the fixing nip region 15c. In the paper non-passing region on
the surface of the fixing belt 25, which the recording paper sheet
32 does not contact, since heat generated from the heat generating
layer 212 will not be taken by the recording paper sheet 32, a
regional part of the resistance heat generating element 301 that
corresponds to the paper non-passing region becomes an excessive
temperature rising state. In this way, when the resistance heat
generating element 301 becomes the excessive temperature rising
state regionally corresponding to the paper non-passing region,
there is a case where the overheat preventing element 40 that
detects the overheated state of the resistance heat generating
element 301 operates erroneously.
[0138] Contrary to this, in the fixing device 15, since the
configuration is such that energization to the resistance heat
generating element 301 is controlled by the overheat preventing
element 40 provided in the vicinity of the detecting section 301b
arranged on the end portion of the axial direction of the heat
generating member 211 corresponding to the paper non-contacting
region of the recording paper sheet 32 of the fixing belt 25,
irrespective of the size of the recording paper sheet 32 to be
supplied to the fixing nip region 15c, the overheated state of the
paper passing region heating section 301a is able to be indirectly
detected from the temperature change in the detecting section 301b
corresponding to the paper non-passing region of the fixing belt 25
which the recording paper sheet 32 does not contact all the time,
and thereby it is possible to prevent that the overheat preventing
element 40 operates erroneously.
[0139] Furthermore, since the paper passing region heating section
301a and the detecting section 301b are electrically connected in
parallel, the resistance heat generating element 301 that generates
heat due to being energized is prevented from being subjected to a
disturbance factor such as variation in applied voltage to the
paper passing region heating section 301a and the detecting section
301b. Thereby, when the resistance heat generating element 301 is
energized, the temperature changes in the paper passing region
heating section 301a and the detecting section 301b are the same,
and the overheated state of the paper passing region heating
section 301a is able to be indirectly detected by the overheat
preventing element 40 accurately from the temperature change in the
detecting section 301b due to energization. Therefore, it is
possible to prevent the paper passing region heating section 301a
of the resistance heat generating element 301 from becoming an
overheated state and resulting in smoke generation, ignition or
burnout, and high safety is able to be secured.
[0140] Moreover, in the resistance heat generating element 301 that
generates heat due to being energized, the paper passing region
heating section 301a and the detecting section 301b preferably have
an equivalent power density. Thereby, when the resistance heat
generating element 301 is energized, the temperature changes in the
paper passing region heating section 301a and the detecting section
301b are the same, and thereby the overheated state of the paper
passing region heating section 301a is able to be indirectly
detected by the overheat preventing element 40 accurately from the
temperature change in the detecting section 301b due to
energization.
[0141] Here, the configuration in which the paper passing region
heating section 301a and the detecting section 301b have an
equivalent power density is that the power density of the detecting
section 301b to the power density of the paper passing region
heating section 301a is adjusted to be in a range of (power density
of the paper passing region heating section.+-.10%), preferably
(power density of the paper passing region heating section+10%). By
adjusting the power density of the detecting section 301b to the
power density of the paper passing region heating section 301a to
be in a range of (power density of the paper passing region heating
section+10%), the temperature change in the detecting section 301b
becomes equivalent to or more than the paper passing region heating
section 301a, and thereby in indirectly detecting the overheated
state of the paper passing region heating section 301a from the
temperature change in the detecting section 301b due to
energization, it is possible to detect the overheated state of the
paper passing region heating section 301a further earlier.
[0142] Additionally, in the resistance heat generating element 301
that generates heat due to being energized, the paper passing
region heating section 301a and the detecting section 301b may be
configured to have an equivalent temperature rising speed in
generating heat due to being energized. Whereby, when the
resistance heat generating element 301 is energized, the
temperature changes in the paper passing region heating section
301a and the detecting section 301b are the same, and thereby the
overheated state of the paper passing region heating section 301a
is able to be indirectly detected by the overheat preventing
element 40 accurately from the temperature change in the detecting
section 301b due to energization.
[0143] Here, the configuration in which the paper passing region
heating section 301a and the detecting section 301b have an
equivalent temperature rising speed is that the temperature rising
speed of the detecting section 301b to the temperature rising speed
of the paper passing region heating section 301a is adjusted to be
in a range of (temperature rising speed of the paper passing region
heating section.+-.10%), preferably (temperature rising speed of
the paper passing region heating section+10%). By adjusting the
temperature rising speed of the detecting section 301b to the
temperature rising speed of the paper passing region heating
section 301a to be in a range of (temperature rising speed of the
paper passing region heating section+10%), the temperature change
in the detecting section 301b becomes equivalent to or more than
the paper passing region heating section 301a, and thereby in
indirectly detecting the overheated state of the paper passing
region heating section 301a from the temperature change in the
detecting section 301b due to energization, it is possible to
detect the overheated state of the paper passing region heating
section 301a further earlier.
[0144] Furthermore, in the resistance heat generating element 301
that generates heat due to being energized, the paper passing
region heating section 301a and the detecting section 301b may be
configured to have an equivalent specific heat capacity. Whereby,
when the resistance heat generating element 301 is energized, the
temperature changes in the paper passing region heating section
301a and the detecting section 310b are the same, and the
overheated state of the paper passing region heating section 301a
is able to be indirectly detected by the overheat preventing
element 40 accurately from the temperature change in the detecting
section 301b due to energization.
[0145] Here, the configuration in which the paper passing region
heating section 301a and the detecting section 301b have an
equivalent specific heat capacity is that the specific heat
capacity of the detecting section 301b to the specific heat
capacity of the paper passing region heating section 301a is
adjusted to be in a range of (specific heat capacity of the paper
passing region heating section.+-.10%), preferably (specific heat
capacity of the paper passing region heating section+10%). By
adjusting the specific heat capacity of the detecting section 301b
to the specific heat capacity of the paper passing region heating
section 301a to be in a range of (specific heat capacity of the
paper passing region heating section+10%), the temperature change
in the detecting section 301b becomes equivalent to or more than
the paper passing region heating section 301a, and thereby in
indirectly detecting the overheated state of the paper passing
region heating section 301a from the temperature change in the
detecting section 301b due to energization, it is possible to
detect the overheated state of the paper passing region heating
section 301a further earlier.
[0146] As described above, the configuration in which the power
density is equivalent, the configuration in which the temperature
rising speed is equivalent, and the configuration in which the
specific heat capacity is equivalent, where the temperature changes
in the paper passing region heating section 301a and the detecting
section 301b are the same, are able to be realized by adjusting an
amount of generating heat, electrical resistance, a material, a
thickness, an area and the like of the detecting section 301b to
the paper passing region heating section 301a in consideration of
the surrounding environment in which the overheat preventing
element 40 is arranged. Furthermore, temperature detecting
capability of the detecting section 301b by the overheat preventing
element 40 may be adjusted by coating (or attaching) a material
which is able to adjust (increase or reduce) the thermal
conductivity on the surface of the detecting section 301b
(detecting surface).
[0147] In addition, as the resistance heat generating element 301,
it is preferable to use one having positive resistance-temperature
property (Positive Temperature Coefficient, abbreviated as PTC
property). In the resistance heat generating element 301 having the
positive resistance-temperature property, electrical resistance
increases as temperature rises. In such a resistance heat
generating element 301 having the positive resistance-temperature
property, when the temperature thereof becomes a predetermined
temperature or more, the electrical resistance sharply increases
and the current value becomes small, thereby becoming the
overheated state is prevented. Moreover, in the resistance heat
generating element 301 having the positive resistance-temperature
property, since the current value becomes small as the temperature
rises, amount of power consumption is able to be reduced and the
energy saving is able to be realized. Moreover, since the
resistance heat generating element 301 has the paper passing region
heating section 301a and the detecting section 301b, even though
the resistance heat generating element 301 is the heat generating
element having the positive resistance-temperature property, it is
possible to indirectly detect the overheated state of the paper
passing region heating section 301a accurately from the temperature
change in the detecting section 301b due to energization.
[0148] In addition, as the resistance heat generating element 301,
one having negative resistance-temperature property (Negative
Temperature Coefficient, abbreviated as NTC property) may be used.
In the resistance heat generating element 301 having negative
resistance-temperature property, electrical resistance decreases as
temperature rises. Here, since the resistance heat generating
element 301 has the paper passing region heating section 301a and
the detecting section 301b, even though the resistance heat
generating element 301 is the heat generating element having the
negative resistance-temperature property, it is possible to
indirectly detect the overheated state of the paper passing region
heating section 301a accurately from the temperature change in the
detecting section 301b due to energization.
[0149] Moreover, as the resistance heat generating element 301, one
having the positive resistance-temperature property and the
negative resistance-temperature property may be used. Here, since
the resistance heat generating element 301 has the paper passing
region heating section 301a and the detecting section 301b, even
though the resistance heat generating element 301 is the heat
generating element having the positive resistance-temperature
property and the negative resistance-temperature property, it is
possible to indirectly detect the overheated state of the paper
passing region heating section 301a accurately from the temperature
change in the detecting section 301b due to energization. The
resistance heat generating element 301 having the positive
resistance-temperature property and the negative
resistance-temperature property is a heat generating element (also
referred to as a PTC ceramic heater) which has the negative
resistance-temperature property around the normal temperature, and
has the positive resistance-temperature property from around a
predetermined temperature, and in which when the temperature rises
further, a change rate of the electrical resistance is great even
with the positive resistance-temperature property.
[0150] FIG. 6 is a view showing a configuration of the heat
generating layer 310 formed by a plurality of resistance heat
generating elements. A heat generating layer of the heat generating
member 211 is able to be configured as the heat generating layer
310 whose heat generating part that generates heat due to being
energized is divided into more than one. The heat generating layer
310 shown in FIG. 6 is composed of a plurality of resistance heat
generating elements 311, 312 and 313. The resistance heat
generating elements 311, 312 and 313 repeat a flexion for a
plurality of times so as to form a fixed surface as a whole. Then,
the heat generating layer 310 is divided into a first heat
generating region composed of the paper passing region heating
section 312a of the resistance heat generating element 312, a
second heat generating region composed of the paper passing region
heating section 313a of the resistance heat generating element 313,
and a third heat generating region composed of the paper passing
region heating section 311a of the resistance heat generating
element 311, corresponding to the plurality of regions on the
surface of the heat radiating member 210. In the embodiment,
assuming a case where the recording paper sheet 32 of different
sizes is passed and printing is performed, the surface of the heat
radiating member 210 that heats the fixing belt 25 which contacts
the recording paper sheet 32 is divided into three regions which
are the both end portions and the central portion in the
longitudinal direction thereof. Then, the first heat generating
region and the second heat generating region of the heat generating
layer 310 correspond respectively to the both end portions in the
longitudinal direction of the heat radiating member 210, and the
third heat generating region corresponds to the central portion in
the longitudinal direction of the heat radiating member 210.
[0151] The detecting section 312b that is electrically connected in
parallel with the paper passing region heating section 312a of the
resistance heat generating element 312, and the detecting section
313b that is electrically connected in parallel with the paper
passing region heating section 313a of the resistance heat
generating element 313 are provided on another end portion of the
axial direction (longitudinal direction) of the heat generating
member 211 corresponding to the non-contact region of the recording
paper sheet 32 of the fixing belt 25. Note that, in the embodiment,
the detecting section 312b and the detecting section 313b are
common. Furthermore, the detecting section 311b that is
electrically connected in parallel with the paper passing region
heating section 311a of the resistance heat generating element 311,
is provided on one end portion of the axial direction (longitudinal
direction) of the heat generating member 211 corresponding to the
non-contact region of the recording paper sheet 32 of the fixing
belt 25. Then, the overheat preventing element 40 is respectively
provided in a vicinity of the detecting sections 312b and 313b
which are common to the resistance heat generating element 312 and
the resistance heat generating element 313, and of the detecting
section 311b of the resistance heat generating element 311.
[0152] The resistance heat generating element 311 is connected to
the power feeding terminal section 221a, the resistance heat
generating element 312 and the resistance heat generating element
313 are connected to the power feeding terminal section 221b, and
thereby it is possible to energize the respective heat generating
regions separately. Whereby, on/off of energization can be switched
for the respective resistance heat generating elements 311, 312,
and 313 corresponding to the respective divisions of the heat
generating part, and the temperature distribution on the surface of
the heat radiating member 210 coming into contact with the fixing
belt 25 is able to be adjusted to desired temperature distribution.
For example, in a case or the like where the recording paper sheet
32 of different dimension, width, or thickness is supplied to the
fixing nip region 15c to fix the toner image 31, by switching
on/off of energization so that only the resistance heat generating
element corresponding to a desired specific region on the surface
of the heat radiating member 210 generates heat corresponding to
the different sizes (dimension, width, or thickness) of the
recording paper sheet 32, the surface of the heat radiating member
210 is able to have the desired temperature distribution. Whereby,
it is possible to suppress the regional abnormal temperature rise
of the resistance heat generating element corresponding to the
non-contact part of the recording paper sheet 32 on the surface of
the fixing belt 25.
[0153] Furthermore, each of the plurality of resistance heat
generating elements 311, 312, and 313 has a paper passing region
heating section and a detecting section to be electrically
connected in parallel. Whereby, it is possible to indirectly detect
an overheat state of the paper passing region heating section by
the overheat preventing element 40 accurately from the temperature
change in the detecting section due to energization for the
resistance heat generating elements 311, 312 and 313 corresponding
to the respective divisions of the heat generating part. Therefore,
it is possible to prevent that the paper passing region heating
section of each of the resistance heat generating elements 311,
312, and 313 becomes the overheated state and results in smoke
generation or burnout, and high safety is able to be secured.
[0154] The configuration of the paper passing region heating
section of the resistance heat generating element in a heat
generating layer of the heat generating member 211 is not limited
to the configuration described above, and it may be configured as
follows, for example. Although description will be given
specifically using FIGS. 7A and 7B, 8A to 8D, 9A and 9B, and 10A
and 10B, the configuration of the heat generating layer shown below
shows a modified example of the paper passing region heating
section, and the configuration other than that is the same as that
of the above-described heat generating layer 212.
[0155] FIGS. 7A and 7B are views showing a divided state of the
paper passing region heating section of the resistance heat
generating element in the heat generating layer. In the heat
generating layer 315 shown in FIG. 7A, paper passing region heating
sections 315a that correspond to the plurality of resistance heat
generating elements extending in the longitudinal direction of the
heat radiating member 210 are arrayed so as to be spaced mutually
in the circumferential direction (short-side direction) of the heat
radiating member 210. Then, when voltage is applied to the power
feeding terminal section 221, each of the plurality of paper
passing region heating sections 315a generate heat separately. That
is, a heat generating part on the surface of the heat generating
layer 315 becomes a state which is divided in association with each
of the paper passing region heating sections 315a that generate
heat separately. In this manner, heat generated from each of the
paper passing region heating sections 315a that generate heat
separately is transmitted to the heat radiating member 210, and
further transmitted from the heat radiating member 210 to the
fixing belt 25 so as to heat the fixing belt 25.
[0156] Additionally, in the heat generating layer 320 shown in FIG.
7B, paper passing region heating sections 320a that correspond to
the plurality of resistance heat generating elements extending in
the short-side direction of the heat radiating member 210 are
arrayed so as to be spaced mutually in the longitudinal direction
of the heat radiating member 210. Then, when voltage is applied to
the power feeding terminal section 221, each of the plurality of
paper passing region heating sections 320a generate heat
separately.
[0157] FIGS. 8A to 8D are views showing another example of a
divided state of the paper passing region heating section. The heat
generating layer 321 shown in FIG. 8A is divided into a first heat
generating region 321a, a second heat generating region 321b, and a
third heat generating region 321c, corresponding to the plurality
of regions on the surface of the heat radiating member 210. In the
embodiment, assuming a case where the recording paper sheet 32 of
different sizes is passed to perform printing, the surface of the
heat radiating member 210 that heats the fixing belt 25 which
contacts the recording paper sheet 32 is divided into three regions
which are both end portions and a central portion in the
longitudinal direction thereof. Then, the first heat generating
region 321a and the second heat generating region 321b of the heat
generating layer 321 respectively correspond to the both end
portions in the longitudinal direction of the heat radiating member
210, and the third heat generating region 321c corresponds to the
central portion in the longitudinal direction of the heat radiating
member 210.
[0158] In the first heat generating region 321a, paper passing
region heating sections 3211a that correspond to the plurality of
resistance heat generating elements extending in the longitudinal
direction of the heat radiating member 210 are provided side by
side so as to be spaced mutually in the short-side direction of the
heat radiating member 210, and both end portions in the
longitudinal direction of each of the paper passing region heating
sections 3211a are connected to a pair of power feeding terminal
sections 221c. In the second heat generating region 321b, paper
passing region heating sections 3211b that correspond to the
plurality of resistance heat generating elements extending in the
longitudinal direction of the heat radiating member 210 are
provided side by side so as to be spaced mutually in the short-side
direction of the heat radiating member 210, and both end portions
in the longitudinal direction of each of the paper passing region
heating sections 3211b are connected to a pair of power feeding
terminal sections 221d. In the third heat generating region 321c,
paper passing region heating sections 3211c that correspond to the
plurality of resistance heat generating elements extending in the
longitudinal direction of the heat radiating member 210 are
provided side by side so as to be spaced mutually in the short-side
direction of the heat radiating member 210, and both end portions
in the longitudinal direction of each of the paper passing region
heating sections 3211c are connected to a pair of power feeding
terminal sections 221e.
[0159] That is, the respective paper passing region heating
sections 3211a in the first heat generating region 321a, the
respective paper passing region heating sections 3211b in the
second heat generating region 321b, and the respective paper
passing region heating sections 3211c in the third heat generating
region 321c, are respectively connected to different power feeding
terminal sections 221c, 221d, and 221e, and thereby it is possible
to energize the respective heat generating regions separately.
Whereby, when the recording paper sheet 32 of different sizes is
passed to perform printing, in order to obtain desired temperature
distribution on the surface of the heat generating layer 321
corresponding to the different passing paper sizes, on/off of the
respective heat generating regions 321a, 321b, and 321c is switched
to perform sub-control of heating so that only a desired specific
region on the surface of the heat generating layer 321 generates
heat, and thereby it is possible to suppress the regional abnormal
temperature rise of the paper passing region heating section in the
heat generating region corresponding to the both end portions of
the passing paper width of the recording paper sheet 32. In this
way, by switching on/off of energization for the respective divided
heat generating regions to perform sub-control of heating, and
suppressing the regional abnormal temperature rise of the paper
passing region heating section of the resistance heat generating
element, fixing failure and degradation in fixed image are able to
be prevented as well as the breakage of the resistance heat
generating element itself is prevented, and an increase of power
consumption is able to be prevented. Moreover, since it is possible
to switch on/off of energization of the heat generating region to
be divided in association with a region that needs heating on the
surface of the fixing belt 25 and perform sub-control of heating
for a different operation mode, it is possible to suppress a
temperature ripple or sharp lowering of temperature after shifted
to an operation mode.
[0160] A heat generating layer 322 shown in FIG. 8B is divided into
a first heat generating region 322a, a second heat generating
region 322b, and a third heat generating region 322c, corresponding
to the plurality of regions on the surface of the heat radiating
member 210. In the embodiment, assuming a case where the recording
paper sheet 32 of different sizes is passed to perform printing,
the surface of the heat radiating member 210 that heats the fixing
belt 25 which contacts the recording paper sheet 32 is divided into
three regions which are both end portions and a central portion in
the longitudinal direction thereof. Then, the first heat generating
region 322a and the second heat generating region 322b of the heat
generating layer 322 respectively correspond to the both end
portions in the longitudinal direction of the heat radiating member
210, and the third heat generating region 322c corresponds to the
central portion in the longitudinal direction of the heat radiating
member 210.
[0161] In the first heat generating region 322a, paper passing
region heating sections 3221a that correspond to the plurality of
resistance heat generating elements extending in the short-side
direction of the heat radiating member 210 are provided side by
side so as to be spaced mutually in the longitudinal direction of
the heat radiating member 210, and both end portions in the
short-side direction of each of the paper passing region heating
sections 3221a are connected to a pair of power feeding terminal
sections 221f. In the second heat generating region 322b, paper
passing region heating sections 3221b that correspond to the
plurality of resistance heat generating elements extending in the
short-side direction of the heat radiating member 210 are provided
side by side so as to be spaced mutually in the longitudinal
direction of the heat radiating member 210, and both end portions
in the short-side direction of each of the paper passing region
heating sections 3221b are connected to a pair of power feeding
terminal sections 221g. In the third heat generating region 322c,
paper passing region heating sections 3221c that correspond to the
plurality of resistance heat generating elements extending in the
short-side direction of the heat radiating member 210 are provided
side by side so as to be spaced mutually in the longitudinal
direction of the heat radiating member 210, and both end portions
in the short-side direction of each of the paper passing region
heating sections 3221c are connected to a pair of power feeding
terminal sections 221h.
[0162] That is, the respective paper passing region heating
sections 3221a in the first heat generating region 322a, the
respective paper passing region heating sections 3221b in the
second heat generating region 322b, and the respective paper
passing region heating sections 3221c in the third heat generating
region 322c, are respectively connected to different power feeding
terminal sections 221f, 221g, and 221h, and thereby it is possible
to energize the respective heat generating regions separately.
Whereby, when the recording paper sheet 32 of different sizes is
passed to perform printing, in order to obtain the desired
temperature distribution on the surface of the heat generating
layer 322 corresponding to the different passing paper sizes,
on/off of energization is switched for the respective heat
generating regions 322a, 322b, and 322c to perform sub-control of
heating so that only a desired specific region on the surface of
the heat generating layer 322 generates heat, and thus it is
possible to suppress the regional abnormal temperature rise of the
paper passing region heating section of the resistance heat
generating element in the heat generating region corresponding to
the both end portions of the passing paper width of the recording
paper sheet 32.
[0163] A heat generating layer 323 shown in FIG. 8C is divided into
a first heat generating region 323a, a second heat generating
region 323b, and a third heat generating region 323c, corresponding
to the plurality of regions on the surface of the heat radiating
member 210. In the embodiment, assuming a case where the recording
paper sheet 32 of different sizes is passed to perform printing,
the surface of the heat radiating member 210 that heats the fixing
belt 25 which contacts the recording paper sheet 32 is divided into
three regions which are both end portions and a central portion in
the longitudinal direction thereof. Then, the first heat generating
region 323a and the second heat generating region 323b of the heat
generating layer 323 respectively correspond to the both end
portions in the longitudinal direction of the heat radiating member
210, and the third heat generating region 323c corresponds to the
central portion in the longitudinal direction of the heat radiating
member 210.
[0164] In the first heat generating region 323a, paper passing
region heating sections 3231a that correspond to the plurality of
resistance heat generating elements extending in the longitudinal
direction of the heat radiating member 210 are provided side by
side so as to be spaced mutually in the short-side direction of the
heat radiating member 210, and both end portions in the short-side
direction of each of the paper passing region heating sections
3231a are connected to a pair of power feeding terminal sections
221i. At this time, the power feeding terminal section 221i on an
end portion side is formed as extending in the short-side direction
of the heat radiating member 210, and the power feeding terminal
section 221i on a center side is formed as extending in a direction
of inclining at a predetermined angle with respect to the
longitudinal direction of the heat radiating member 210. In the
second heat generating region 323b, paper passing region heating
sections 3231b that correspond to the plurality of resistance heat
generating elements extending in the longitudinal direction of the
heat radiating member 210 are provided side by side so as to be
spaced mutually in the short-side direction of the heat radiating
member 210, and both end portions in the short-side direction of
each of the paper passing region heating sections 3231b are
connected to a pair of power feeding terminal sections 221j. At
this time, the power feeding terminal section 221j on an end
portion side is formed as extending in the short-side direction of
the heat radiating member 210, and the power feeding terminal
section 221j on a center side is formed as extending in a direction
of inclining at a predetermined angle with respect to the
longitudinal direction of the heat radiating member 210. In the
third heat generating region 323c, paper passing region heating
sections 3231c that correspond to the plurality of resistance heat
generating elements extending in the longitudinal direction of the
heat radiating member 210 are provided side by side so as to be
spaced mutually in the short-side direction of the heat radiating
member 210, and both end portions in the short-side direction of
each of the paper passing region heating sections 3231c are
connected to a pair of power feeding terminal sections 221k. At
this time, the power feeding terminal sections 221k are provided to
be parallel with the terminals on the center sides of the power
feeding terminal section 221i and the power feeding terminal
section 221j.
[0165] That is, the respective paper passing region heating
sections 3231a in the first heat generating region 323a, the
respective paper passing region heating sections 3231b in the
second heat generating region 323b, and the respective paper
passing region heating sections 3231c in the third heat generating
region 323c, are respectively connected to different power feeding
terminal sections 221i, 221j, and 221k, and thereby it is possible
to energize the respective heat generating regions separately.
Whereby, when the recording paper sheet 32 of different sizes is
passed to perform printing, in order to obtain desired temperature
distribution on the surface of the heat generating layer 323
corresponding to the different passing paper sizes, on/off of
energization is switched for the respective heat generating regions
323a, 323b, and 323c to perform sub-control of heating so that only
a desired specific region on the surface of the heat generating
layer 323 generates heat, and thus it is possible to suppress the
regional abnormal temperature rise of the paper passing region
heating section of the resistance heat generating element in the
heat generating region corresponding to the both end portions of
the passing paper width of the recording paper sheet 32.
[0166] A heat generating layer 324 shown in FIG. 8D is divided into
a first heat generating region 324a, a second heat generating
region 324b, and a third heat generating region 324c, corresponding
to the plurality of regions on the surface of the heat radiating
member 210. In the embodiment, the surface of the heat radiating
member 210 is divided into three regions which are two regions on
an end side in the longitudinal direction thereof and the remaining
region. Then, the first heat generating region 324a of the heat
generating layer 324 corresponds to the remaining region of the
heat radiating member 210, and the second heat generating region
324b corresponds to a center-side region among two regions on the
end side in the longitudinal direction of the heat radiating member
210, and the third heat generating region 324c corresponds to an
end portion-side region among the two regions on the end side in
the longitudinal direction of the heat radiating member 210.
[0167] In the first heat generating region 324a, paper passing
region heating sections 3241a that correspond to the plurality of
resistance heat generating elements extending in the longitudinal
direction of the heat radiating member 210 are provided side by
side so as to be spaced mutually in the short-side direction of the
heat radiating member 210, and both end portions in the short-side
direction of each of the paper passing region heating sections
3241a are connected to a pair of power feeding terminal sections
221l. In the second heat generating region 324b, paper passing
region heating section 3241b that correspond to the plurality of
resistance heat generating elements extending in the longitudinal
direction of the heat radiating member 210 are provided side by
side so as to be spaced mutually in the short-side direction of the
heat radiating member 210, and both end portions in the short-side
direction of each of the paper passing region heating sections
3241b are connected to a pair of power feeding terminal sections
221m. In the third heat generating region 324c, paper passing
region heating sections 3241c that correspond to the plurality of
resistance heat generating elements extending in the longitudinal
direction of the heat radiating member 210 are provided side by
side so as to be spaced mutually in the short-side direction of the
heat radiating member 210, and both end portions in the short-side
direction of each of the paper passing region heating sections
3241c are connected to a pair of power feeding terminal sections
221n.
[0168] That is, the respective paper passing region heating
sections 3241a in the first heat generating region 324a, the
respective paper passing region heating sections 3241b in the
second heat generating region 324b, and the respective paper
passing region heating sections 3241c in the third heat generating
region 324c, are respectively connected to different power feeding
terminal sections 221i, 221m, and 221n, and thereby it is possible
to energize the respective heat generating regions separately.
Whereby, in order to obtain desired temperature distribution on the
surface of the heat generating layer 324, on/off of energization is
switched for the respective heat generating regions 324a, 324b, and
324c and it is possible to perform sub-control of heating so that
only a desired specific region on the surface of the heat
generating layer 324 generates heat.
[0169] In the above embodiments, although descriptions have been
given for the divided state of the heat generating part on the
surface of the heat generating layer that the paper passing region
heating sections corresponding to the plurality of resistance heat
generating elements are formed on a same layer, hereinafter, using
FIGS. 9A and 9B, description will be given for a divided state of a
heat generating part on a surface of a heat generating layer having
a layered structure in which a plurality of resistance heat
generating elements are layered.
[0170] FIGS. 9A and 9B are views showing a divided state of a paper
passing region heating section in a heat generating layer having a
layered structure in which a plurality of resistance heat
generating elements are layered. FIG. 9A shows a configuration of a
heat generating layer 325 having a layered structure in which a
plurality of resistance heat generating elements are layered, and
FIG. 9B shows an arranged state of the paper passing region heating
section of each of the resistance heat generating elements in a
plan view of the layered structure of the resistance heat
generating elements in the heat generating layer 325.
[0171] The heat generating layer 325 shown in FIGS. 9A and 9B is
formed by laminating a plurality of ceramic sheets having a width
of 12 mm corresponding to the circumferential direction of the heat
radiating member 325, providing a silver-palladium-based thin-film
resistance heating element having a line width of 1 mm on the
matching surface of each ceramic sheet so as to reciprocate and
turn back 2.5 times by printing, and firing the thin-film
resistance heating element. The size of the respective ceramic
sheets, and the material, width, thickness, and the turnback
pattern at the time of printing of the thin-film resistance heating
element are appropriately set in accordance with the necessary heat
generation capability of the heat generating layer 325. The heat
generating layer 325 including a ceramic heating element laminated
with ceramic sheets can be rapidly heated, and even when the heat
generating layer 325 itself is in the overheated state, safety is
ensured since smoking or firing does not occur while damages
occur.
[0172] The heat generating layer 325 is divided into a first heat
generating region 325a, a second heat generating region 325b, and a
third heat generating region 325c, corresponding to the plurality
of regions of the surface of the heat radiating member 210. In this
embodiment, on the assumption that printing is performed on the
recording paper sheets 32 of different sizes, the surface of the
heat radiating member 210, which heats the fixing belt 25 in
contact with the recording paper sheets 32, is divided into three
regions which are both end portions and a central portion in the
longitudinal direction thereof. Then, the first heat generating
region 325a and the second heat generating region 325b of the heat
generating layer 325 correspond to both end portions in the
longitudinal direction of the heat radiating member 210, and the
third heat generating region 325c corresponds to the central
portion in the longitudinal direction of the heat radiating member
210.
[0173] The heat generating layer 325 has the layered structure in
which the first heat generating region 325a and the second heat
generating region 325b are formed in a same layer, and the third
heat generating region 325c is formed in another layer. In the
first heat generating region 325a, a paper passing region heating
section 3251a that corresponds to the resistance heat generating
element extending as a wave-shape in the short-side direction of
the heat radiating member 210, and both end portions in the
short-side direction of the paper passing region heating section
3251a are connected to a pair of power feeding terminal sections
221o. In the second heat generating region 325b, a paper passing
region heating section 3251b that corresponds to the resistance
heat generating element extending as a wave-shape in the short-side
direction of the heat radiating member 210, and both end portions
in the short-side direction of the paper passing region heating
section 3251b are connected to a pair of power feeding terminal
sections 221p. In the third heat generating region 325c, a paper
passing region heating section 3251c that corresponds to the
resistance heat generating element extending as a wave-shape in the
short-side direction of the heat radiating member 210, and both end
portions in the short-side direction of the paper passing region
heating section 3251c are connected to a pair of power feeding
terminal sections 221q.
[0174] That is, the paper passing region heating section 3251a in
the first heat generating region 325a, the paper passing region
heating section 3251b in the second heat generating region 325b,
and the paper passing region heating section 3251c in the third
heat generating region 325c, are respectively connected to
different power supply terminal sections 221o, 221p, and 221q, and
thereby it is possible to energize the respective heat generating
regions separately. Whereby, when the recording paper sheet 32 of
different sizes is passed to perform printing, in order to obtain
desired temperature distribution on the surface of the heat
generating layer corresponding to the different passing papar
sizes, on/off of energization is switched for the respective heat
generating regions 325a, 325b, and 325c to perform sub-control of
heating so that only a desired specific region on the surface of
the heat generating layer 325 generates heat, and thus it is
possible to suppress the regional abnormal temperature rise of the
paper passing region heating section of the resistance heat
generating element in the heat generating region corresponding to
the both end portions of the passing paper width of the recording
paper sheet 32.
[0175] FIGS. 10A and 10B are views showing a configuration of the
heating member having a structure in which a plurality of
semiconductor ceramic elements are held by a heat radiating
member.
[0176] A heating member 326 shown in FIG. 10A has a structure in
which a plurality of semiconductor ceramic elements 326a are
sandwiched by two heat radiating members 326b. Each of the
semiconductor ceramic elements 326a is a resistance heat generating
element that generates heat due to being energized. In the
embodiment, a detecting section of the resistance heat generating
element is provided by being electrically connected in parallel
with each semiconductor ceramic element 326a. Each of the heat
radiating members 326b has a curved section 326c which is curved
and a bent section 326d which is formed by bending the curved
section 326c from an end portion of the circumferential direction
thereof. In the heating member 326, in a state of sandwiching the
semiconductor ceramic elements 326a with the bent sections 326d of
the two heat radiating members 326b, the curved sections 326c of
the two heat radiating members 326b are to form a semi-cylinder
shape as a whole. Then, the surface of the curved sections 326c
formed to be a semi-cylinder shape as a whole is a surface of
contacting the fixing belt 25. Each of the semiconductor ceramic
elements 326a is one obtained by molding inorganic powder whose
chief component is barium titanate into a thin block shape and
firing the molded product. It is possible to obtain the heat
generation amount of more than ten watts to hundreds of watts per
each of the semiconductor ceramic elements 326a.
[0177] A heating member 327 shown in FIG. 10B has a structure in
which a plurality of semiconductor ceramic elements 327a are fit
into the heat radiating member 327b. Each of the semiconductor
ceramic elements 327a is a resistance heat generating element that
generates heat due to being energized. In the embodiment, a
detecting section of the resistance heat generating element is
provided by being electrically connected in parallel with each
semiconductor ceramic element 327a. The heat radiating member 327b
includes a curved section 327c which is curved and formed to be a
semi-cylinder shape, and a protruding section 327d which protrudes
from the inner circumferential surface of the curved section 327c
and has a recess. In the heating member 327, each of the
semiconductor ceramic elements 327a is fit into the recess provided
in the protruding section 327d of the heating member 327b. Then,
the outer circumferential surface of the curved section 327c of the
heat radiating member 327b is a surface of contacting the fixing
belt 25.
[0178] FIG. 11 is a view showing a configuration of a fixing device
440 according to a second embodiment of the invention. The fixing
device 440 is a fixing device of two-stage fixing type, and
includes a first fixing section 450 that performs primary fixing of
an unfixed toner image 31 onto the recording paper sheet 32 under
application of heat and pressure, and a second fixing section 460
that is arranged on a downstream side of a conveyance direction of
the recording paper sheet 32 with respect to the first fixing
section 450 and performs secondary fixing of the toner image 31
after the primary fixing onto the recording paper sheet 32 under
application of heat and pressure, and is configured such that the
first fixing section 450 and the second fixing section 460 are
arranged side by side in a horizontal direction. Then the first
fixing section 450 and the second fixing section 460 of the fixing
device 440 are the above-described fixing device 15 of the
embodiment including the heating member having the heat generating
layer composed of the resistance heat generating element configured
such that the paper passing region heating section and the
detecting section are electrically connected in parallel.
[0179] In the fixing device 440 of two-stage fixing type thus
configured, when the respective resistance heat generating elements
provided in the first fixing section 450 and the second fixing
section 460 are energized, temperature changes in the paper passing
region heating section and the detecting section of each of the
resistance heat generating elements are the same. Therefore, in
each of the resistance heat generating elements provided in the
first fixing section 450 and the second fixing section 460, the
overheated state of the paper passing region heating section is
able to be indirectly detected accurately from the temperature
change in the detecting section due to energization.
[0180] Accordingly, it is possible to accurately detect by the
overheat preventing element 40 that at least either one of the
paper passing region heating sections of each of the resistance
heat generating elements provided in the first fixing section 450
and the second fixing section 460 becomes an overheated state so as
to prevent resulting in smoke generation or burnout and high safety
is able to be secured.
[0181] A guide member such as a conveyance guide plate or a
conveying roller, is provided between the first fixing section 450
and the second fixing section 460. The recording paper sheet 32
that is subjected to fixing in the fixing nip region of the first
fixing section 450, is conveyed along the guide member, is
subjected to fixing in the fixing nip region of the second fixing
section 460, and then discharged. The fixing device 440 can be
mounted in the image forming apparatus 100, instead of the fixing
device 15.
[0182] The first fixing section 450 includes a first heating
section 451, a first fixing roller 452, a first pressure roller
453, and a first fixing belt 454 which is the same as the
above-described fixing belt 25. In the first fixing section 450,
the first fixing belt 454 is supported around the first fixing
roller 452 and the first heating section 451 with tension, and the
first pressure roller 453 is arranged to face the first fixing
roller 452 with the first fixing belt 454 interposed
therebetween.
[0183] The first heating section 451 has the above-described
heating member 21. The heating member 21 of the first heating
section 451 includes the above-described heat radiating member 210,
a heat generating member having the above-described heat generating
layer 310 in which the heat generating region is divided into three
regions which are the both end portions and the central portion in
the longitudinal direction of the heat radiating member 210, and
the above-described inside securing member 218.
[0184] The heating member 210 in the embodiment is made by curving
a metallic thin plate formed of aluminum and having a thickness of
0.5 mm such that a diameter in section is to be 40 mm and an
opening angle of an opening section is to be 125.degree., and
contacts the first fixing belt 454 on the outer circumferential
surface thereof so as to transmit heat generated by the heat
generating layer 310 to the first fixing belt 454.
[0185] As described above, the heat generating layer 310 is divided
into a first heat generating region 310a and a second heat
generating region 310b corresponding to the both end portions in
the longitudinal direction of the heat radiating member 210, and a
third heat generating region 212c corresponding to the central
portion in the longitudinal direction of the heat radiating member
210, and the respective heat generating regions can be energized
separately. By controlling energization of the heat generating
regions appropriately in accordance with the size or thickness of
the recording paper sheet 32, the heat generating layer 310
generates heat. In this embodiment, the heat generating layer 310
generates heat with the amount of heat generation of 1100 W, the
amount of heat generation of the third heat generating region 310c
is 600 W, and the amount of heat generation of each of the first
heat generating region 310a and the second heat generating region
310b is 250 W.
[0186] The inside securing member 218, as described above, is
configured by a spiral-shaped member formed to be a spiral shape,
and holds the heat generating member having the heat generating
layer 310 by being in line-contact with a surface side of a
thickness direction of the heat generating layer 310 so as to
elastically press the heat generating member toward the direction
moving closer to the heat radiating member 210 and by allowing
another surface side of the thickness direction of the heat
generating member 310 to be in surface-contact with the inside
surface of the heat radiating member 210.
[0187] Further, a first heating element-side thermistor 455 is
arranged around the circumferential surface of the first fixing
belt 454 wound around the first heating section 451 and detects
temperature of the circumferential surface in a non-contact
manner.
[0188] The first fixing roller 452 comes into pressure-contact with
the first pressure roller 453 with the first fixing belt 454
interposed therebetween to form the fixing nip region, and is
driven to rotate in a rotation direction G around the rotation axis
by a drive motor (not shown), thereby conveying the first fixing
belt 454. The first fixing roller 452 has a two-layered structure
consisting of a core metal 452a and an elastic layer 452b, which
are formed in this order from inside. For the core metal 452a, for
example, a metal such as iron, stainless steel, aluminum, or
copper, or an alloy thereof is used. In this embodiment, the core
metal 452a is a member formed of aluminum and having an outer
diameter of 40 mm. For the elastic layer 452b, a heat resistant
rubber material such as silicone rubber or fluorine rubber is
appropriately used. In this embodiment, the elastic layer 452b is a
member formed of silicone foaming sponge having small thermal
conductivity and having a thickness of 5 mm. The surface hardness
of the first fixing roller 452 thus configured is 68 degrees (Asker
C hardness).
[0189] Furthermore, a first fixing roller-side thermistor 456 is
arranged around the circumferential surface of the winding portion
(heating nip region) of the first fixing roller 452, at which the
first fixing belt 454 is wound, and detects temperature of the
circumferential surface of the first fixing belt 454 wound around
the first fixing roller 454 in a non-contact manner.
[0190] The first pressure roller 453 is opposite to and in
pressure-contact with the first fixing roller 452 with the first
fixing belt 454 interposed therebetween, and is driven to rotate in
a rotation direction H around the rotation axis by a drive motor
(not shown). The first fixing belt 454 and the first fixing roller
452, and the first pressure roller 453 rotate reversely with
respect to each other. The first pressure roller 453 has a
three-layered structure consisting of a core metal 453a, an elastic
layer 453b, and a release layer 453c, which are formed in this
order from inside. For the core metal 453a, for example, a metal
such as iron, stainless steel, aluminum, or copper, or an alloy
thereof is used. In this embodiment, the core metal 453a is a
member formed of aluminum and having an outer diameter of 46 mm.
For the elastic layer 453b, a heat resistant rubber material such
as silicone rubber or fluorine rubber is appropriately used. In
this embodiment, the elastic layer 453b is a member formed of
silicone rubber and having a thickness 2 mm. For the release layer
453c, fluorine resin such as PFA (a copolymer of
tetrafluoroethylene and perfluoroalkyl vinyl ether) or PTFE
(polytetrafluoroethylene), is appropriately used. Further, the
release layer 453c is a member formed of PFA and having a thickness
of about 30 .mu.m. The surface hardness of the first pressure
roller 453 thus configured is 75 degrees (Asker C hardness).
[0191] Furthermore, a first heater lamp 453d (for example, rated
power 400 W) is arranged in an interior of the first pressure
roller 453 and heats the first pressure roller 453. A control
circuit (not shown) causes power to be supplied (energized) from a
power supply circuit (not shown) to the first heater lamp 453d, the
first heater lamp 453d emits light, and infrared rays are radiated
from the first heater lamp 453d. Thus, the inner circumferential
surface of the first pressure roller 453 absorbs the infrared rays
and is heated, such that the entire first pressure roller 453 is
heated. Further, a first pressure roller-side thermistor 457 is
arranged on the circumferential surface of the first pressure
roller 453 and detects temperature of the circumferential surface
of the first pressure roller 453 in a contact manner. Furthermore,
an external heater for rapidly heating the surface of the first
pressure roller 453, a cleaning roller, and an oil coating roller
may be provided in the first pressure roller 453.
[0192] The first fixing roller 452 and the first pressure roller
453 have an outer diameter of 50 mm and are in pressure-contact
with each other by an elastic member (spring member) (not shown)
with a predetermined load (in this case, 600 N). Thus, the fixing
nip region is formed between the circumferential surface of the
first fixing belt 454 which is supported around the first fixing
roller 452 and the first heating section 451, and the
circumferential surface of the first pressure roller 453. The
fixing nip region refers to a region where the first fixing belt
454 and the first pressure roller 453 come into contact with each
other. In this embodiment, the fixing nip region is 9 mm. The first
fixing roller 452 is heated to a predetermined temperature (in this
case, 180.degree. C.), and the recording paper sheet 32 passes
through the fixing nip region, such that the unfixed toner images
31 are heated and molten, and the images are fixed. When the
recording paper sheet 32 passes through the fixing nip region, the
first fixing belt 454 comes into contact with the toner image
forming surface of the recording paper sheet 32, and the first
pressure roller 453 comes into contact with the surface of the
recording paper sheet 32 opposite to the toner image forming
surface.
[0193] The recording paper sheet 32 is conveyed to the fixing nip
region at a predetermined fixing speed and a copy speed in
accordance with the rotation speed of the first fixing roller 452
and the first pressure roller 453, and the unfixed toner images 31
are fixed onto the recording paper sheet 32 under application of
heat and pressure. The fixing speed refers to a so-called process
speed. In the case of monochrome printing, the fixing speed is 355
mm/sec, and in the case of color printing, the fixing speed is 220
mm/sec. The copy speed refers to the number of copies per minute.
In the case of monochrome printing, the copy speed is 70
sheets/minute, and in the case of color printing, the copy speed is
60 sheets/minute.
[0194] A web cleaner (not shown) for cleaning the surface of the
first fixing belt 454 is arranged in the first fixing section
450.
[0195] The control circuit serving as a temperature control section
controls energization to the heat generating layer 310 and the
first heater lamp 453d through the power supply circuit on the
basis of temperature data detected by the respective thermistors
455, 456, and 457, such that the heat radiating member 210 of the
first heating section 451, the first fixing belt 454, and the first
pressure roller 453 are at a predetermined temperature.
[0196] Next, the second fixing section 460 will be described. The
second fixing section 460 includes a second heating section 461, a
second fixing roller 462, a second pressure roller 463, and a
second fixing belt 464 which is the same as the above-described
fixing belt 25. In the second fixing section 460, the second fixing
belt 464 is supported around the second fixing roller 462 and the
second heating section 461 with tension, and the second pressure
roller 463 is arranged to face the second fixing roller 462 with
the second fixing belt 464 interposed therebetween. The second
fixing section 460 has the same basic configuration as the first
fixing section 450, except that the second heating section 461 is
different from the first heating section 451, and the second fixing
roller 462 is different from the first fixing roller 452.
[0197] The second heating section 461 has the above-described
heating member 21. The heating member 21 of the second heating
section 461 includes the above-described heat radiating member 210
and a heat generating member having a heat generating layer 310 in
which the heat generating region is divided into three regions
which are the both end portions and the central portion in the
longitudinal direction of the heat radiating member 210 and two
regions in the short-side direction of the heat radiating member
210, that is, six regions in total, and the above-described inside
securing member 218.
[0198] The heat radiating member 210 contacts the second fixing
belt 464 on the outer circumferential surface thereof so as to
transmit heat generated by the heat generating layer 310 to the
second fixing belt 464.
[0199] As described above, the heat generating layer 310 is divided
into first to six heat generating regions. The first heat
generating region and the second heat generating region are both
end portions in the longitudinal direction of the heat radiating
member 210 and correspond to the downstream side in the rotation
direction of the second fixing belt 464. The third heat generating
region and the fourth heat generating region are both end portions
in the longitudinal direction of the heat radiating member 210 and
correspond to the upstream side in the rotation direction of the
second fixing belt 464. The fifth heat generating region is the
central portion in the longitudinal direction of the heat radiating
member 210 and corresponds to the downstream side in the rotation
direction of the second fixing belt 464. The sixth heat generating
region is the central portion in the longitudinal direction of the
heat radiating member 210 and corresponds to the upstream side in
the rotation direction of the second fixing belt 464. The
respective heat generating regions can be energized separately. By
controlling energization of the heat generating regions
appropriately in accordance with the size or thickness of the
recording paper sheet 32, the heat generating layer 310 generates
heat. In this embodiment, the heat generating layer 310 generates
heat with the amount of heat amount of 900 W, the amount of heat
generation of the fifth heat generating region is 400 W, the amount
of heat generation of the sixth heat generating region is 200 W,
the amount of heat generation of each of the first heat generating
region and the second heat generating region is 100 W, and the
amount of heat generation of each of the third heat generating
region and the fourth heat generating region is 50 W.
[0200] The inside securing member 218, as described above, is
configured by a spiral-shaped member formed to be a spiral shape,
and holds the heat generating member having the heat generating
layer 310 by being in line-contact with a surface side of a
thickness direction of the heat generating layer 310 so as to
elastically press the heat generating member toward the direction
moving closer to the heat radiating member 210 and by allowing
another surface side of the thickness direction of the heat
generating member 310 to be in surface-contact with the inside
surface of the heat radiating member 210.
[0201] Further, a second heating element-side thermistor 465 is
arranged around the circumferential surface of the second fixing
belt 464 wound around the second heating section 461 and detects
temperature of the circumferential surface in a non-contact
manner.
[0202] The second fixing roller 462 comes into pressure-contact
with the second pressure roller 463 with the second fixing belt 464
interposed therebetween to form the fixing nip region, and is
driven to rotate in a rotation direction I around the rotation axis
by a drive motor (not shown), thereby conveying the second fixing
belt 464. The second fixing roller 462 has a two-layered structure
consisting of a core metal 462a and an elastic layer 462b, which
are formed in this order from inside. For the core metal 462a, for
example, a metal such as iron, stainless steel, aluminum, or
copper, or an alloy thereof is used. In this embodiment, the core
metal 462a is a member formed of aluminum and having an outer
diameter of 46 mm. For the elastic layer 462b, a heat resistant
rubber material such as silicone rubber or fluorine rubber is
appropriately used. In this embodiment, the elastic layer 462b is a
member formed of silicone rubber and having a thickness of 2 mm.
The surface hardness of the second fixing roller 462 thus
configured is 68 degrees (Asker C hardness).
[0203] Furthermore, a second fixing roller-side thermistor 466 is
arranged around the circumferential surface of the winding portion
(heating nip region) of the second fixing roller 462, at which the
second fixing belt 464 is wound, and detects temperature of the
circumferential surface of the second fixing belt 464 wound around
the second fixing roller 462 in a non-contact manner.
[0204] The second pressure roller 463 is opposite to and in
pressure-contact with the second fixing roller 462 with the second
fixing belt 464 interposed therebetween, and is driven to rotate in
a rotation direction J around the rotation axis by a drive motor
(not shown). The second fixing belt 464 and the second fixing
roller 462, and the second pressure roller 463 rotate reversely
with each other. The second pressure roller 463 has a three-layered
structure consisting of a core metal 463a, an elastic layer 463b,
and a release layer 463c, which are formed in this order from
inside. For the core metal 463a, for example, a metal such as iron,
stainless steel, aluminum, or copper, or an alloy thereof is used.
In this embodiment, the core metal 463a is a member formed of
aluminum and having an outer diameter of 46 mm. For the elastic
layer 463b, a heat resistant rubber material such as silicone
rubber or fluorine rubber is appropriately used. In this
embodiment, the elastic layer 463b is a member formed of silicone
rubber and having a thickness of 2 mm. For the release layer 463c,
fluorine resin such as PFA or PTFE is appropriately used. In this
embodiment, the release layer 463c is a member formed of PFA and
having a thickness of about 30 .mu.m. The surface hardness of the
second pressure roller 463 thus configured is 75 degrees (Asker C
hardness).
[0205] Furthermore, a second heater lamp 463d (for example, rated
power 400 W) for heating the second pressure roller 463 is arranged
inside the second pressure roller 463. A control circuit (not
shown) causes power to be supplied (energized) from the power
supply circuit (not shown) to the second heater lamp 463d, the
second heater lamp 463d emits light, and infrared rays are radiated
from the second heater lamp 463d. Thus, the inner circumferential
surface of the second pressure roller 463 absorbs the infrared rays
and is heated, such that the entire second pressure roller 463 is
heated. Further, a second pressure roller-side thermistor 467 is
arranged on the circumferential surface of the second pressure
roller 463 and detects temperature of the circumferential surface
of the second pressure roller 463 in a contact manner.
[0206] The second fixing roller 462 and the second pressure roller
463 have an outer diameter of 50 mm and are in pressure-contact
with each other by an elastic member (spring member) (not shown)
with a predetermined load (in this case, 550 N). Thus, the fixing
nip region is formed between the circumferential surface of the
second fixing belt 464 which is supported around the second fixing
roller 462 and the second heating section 461, and the
circumferential surface of the second pressure roller 463. The
fixing nip region refers to a portion where the second fixing belt
464 and the second pressure roller 463 come into contact with each
other. In this embodiment, the fixing nip region is 8 mm.
[0207] The control circuit serving as a temperature control section
controls energization to the heat generating layer 310 and the
second heater lamp 463d through the power supply circuit on the
basis of temperature data detected by the respective thermistors
465, 466, and 467, such that the heat radiating member 210 of the
second heating section 461, the second fixing belt 464, and the
second pressure roller 463 are at a predetermined temperature.
[0208] In the above-described fixing device 440 including the first
fixing section 450 and the second fixing section 460, as described
in Japanese Unexamined Patent Publication JP-A 2005-352389, control
is performed such that the temperature of the second fixing section
460 is controlled so as to compensate for the changes in
temperature of the first fixing section 450 (gloss compensation
mode), whereby substantially uniform image gloss is obtained when
the sheet passes successively therethrough (successive fixing
processing).
[0209] First, the relational expression about temperature between
the first fixing belt 454 and the second fixing belt 464 is
calculated in advance such that a plurality of output images have
substantially uniform gloss. That is, the temperature of the second
fixing belt 464 is controlled so as to be at temperature calculated
by the relational expression with respect to the change in
temperature of the first fixing belt 454, such that images with
uniform gloss are obtained, regardless of the temperature of the
first fixing roller 452.
[0210] The temperature control section of the first fixing section
450 calculates the difference (T1-T2) between the surface
temperature T1 of the first fixing belt 454 detected by the first
fixing roller-side thermistor 456 and a target temperature set
value T2 of the first fixing belt 454 as a temperature change value
a of the first fixing belt 454. When the temperature change value a
exceeds a temperature ripple for temperature control of the first
fixing belt 454 when the sheet does not pass therethrough, control
by the gloss correction temperature control mode is performed. When
a target set temperature of the second fixing belt 464 is referred
to as T4, in the gloss correction temperature control mode,
temperature control of the second fixing belt 464 is performed by
means of a value (T4+.beta.), which is obtained by adding a
temperature correction value .beta. of the second fixing belt 464
to the target set temperature T4 of the second fixing belt 464. The
temperature control section of the second fixing section 460
substitutes the surface temperature (T2+.alpha.) of the first
fixing belt 454 into the relational expression to calculate the
control temperature (T4+.beta.) of the second fixing belt 464 and
then performs temperature control. The gloss correction temperature
control mode ends when the successive fixing processing ends or
when the temperature change value .alpha. of the first fixing belt
454 is equal to or lower than a predetermined value, and control by
the normal mode is carried out.
[0211] FIG. 12 is a view showing a configuration of a fixing device
470 according to a third embodiment of the invention. The fixing
device 470 is a fixing device of two-stage fixing type, and
includes a first fixing section 480 that performs primary fixing of
an unfixed toner image 31 onto the recording paper sheet 32 under
application of heat and pressure, and a second fixing section 490
that performs secondary fixing of the toner image 31 after the
primary fixing onto the recording paper sheet 32 under application
of heat and pressure, the second fixing section 490 being
configured by a pair of heating and pressure rollers 491 that are
provided with a heating section in an interior thereof, and are in
pressure-contact with each other, and being arranged on a
downstream side of a conveyance direction of the recording paper
sheet 32 with respect to the first fixing section 480. The fixing
device 470 is configured such that the first fixing section 480 and
the second fixing section 490 are arranged side by side in a
horizontal direction. Then the first fixing section 480 of the
fixing device 470 is the above-described fixing device 15 of the
embodiment including the heating member having the heat generating
layer composed of the resistance heat generating element configured
such that the paper passing region heating section and the
detecting section are electrically connected in parallel.
[0212] In the fixing device 470 of two-stage fixing type thus
configured, when the respective resistance heat generating elements
provided in the first fixing section 480 are energized, temperature
changes in the paper passing region heating section and the
detecting section of each of the resistance heat generating
elements are the same. Therefore, in each of the resistance heat
generating elements provided in the first fixing section 480, the
overheated state of the paper passing region heating section is
able to be indirectly detected accurately from the temperature
change in the detecting section due to energization. Accordingly,
it is possible to accurately detect by the overheat preventing
element 40 that the paper passing region heating section of the
resistance heat generating element provided in the first fixing
section 480 becomes an overheated state so as to prevent resulting
in smoke generation or burnout, and high safety is able to be
secured. Furthermore, although the first fixing section 480 and the
second fixing section 490 are fixing sections whose heating methods
are different from each other, it is possible to detect the
overheated state safely without occurrence of problems such as
detection of only one of the fixing sections is difficult, or the
detection is performed slowly.
[0213] A guide member such as a conveyance guide plate or a
conveying roller, is provided between the first fixing section 480
and the second fixing section 490. The recording paper sheet 32
that is subjected to fixing in the fixing nip region of the first
fixing section 480, is conveyed along the guide member, is
subjected to fixing in the fixing nip region of the second fixing
section 490, and then discharged. The fixing device 470 can be
mounted in the image forming apparatus 100, instead of the fixing
device 15.
[0214] The first fixing section 480 provided in the fixing device
470 has the same configuration as the first fixing section 450
provided in the fixing device 440 described above, and thus
description thereof will not be repeated. The second fixing section
490 provided in the fixing device 470 is a fixing section of roller
fixing type, in which the pair of heating and pressure rollers 491
are in pressure-contact with each other to form the fixing nip
region. The rollers are driven to rotate reversely with respect to
each other.
[0215] The pair of heating and pressure rollers 491 have a
three-layered structure consisting of a core metal 491a, an elastic
layer 491b, and a release layer 491c, which are formed in this
order from inside. For the core metal 491a, for example, a metal
such as iron, stainless steel, aluminum, or copper, or an alloy
thereof is used. For the elastic layer 491b, a heat resistant
rubber material such as silicone rubber or fluorine rubber is
appropriately used. For the release layer 491c, fluorine resin such
as PFA or PTFE is appropriately used.
[0216] Further, each of the pair of heating and pressure rollers
491 is provided with a heater lamp 491d in an interior thereof to
heat the corresponding heating and pressure roller 491. A control
circuit (not shown) causes power to be supplied (energized) from a
power supply circuit (not shown) to the heater lamps 491d, the
heater lamps 491d emit light, and infrared rays are radiated from
the heater lamps 491d. Thus, the inner circumferential surfaces of
the heating and pressure rollers 491 absorb the infrared rays and
are heated, such that the entire heating and pressure rollers 491
are heated. The configuration for heating the heating and pressure
rollers 491 is not limited to that described above, an induction
heating method using induction heating may be used or a heater lamp
and an induction heating method may be appropriately combined.
[0217] In the above-described fixing device 470 including the first
fixing section 480 and the second fixing section 490, the first
fixing section 480 has a mechanism that is capable of carrying out
rapid heating, and the second fixing section 490 has a large heat
capacity.
[0218] In the fixing device 470 thus configured, the first fixing
section 480 is warmed up in advance. Then, when rising is
satisfactory, and a copy operation should be rapidly carried out,
after the recording paper sheet 32 passes through the fixing nip
region of the first fixing section 480 and is subjected to fixing,
the recording paper sheet 32 is conveyed to a bypass route 485
through the guide member and discharged by a plurality of conveying
rollers 485a provided in the bypass route 485. In this case, the
recording paper sheet 32 is subjected to fixing only by the first
fixing section 480. When the recording paper sheet 32 is thin
paper, in the same manner as described above, fixing may be carried
out only by the first fixing section 480.
[0219] Meanwhile, when the recording paper sheet 32 is thick paper,
to improve image gloss or to improve the fixing speed, the
recording paper sheet 32 which is subjected to fixing in the fixing
nip region of the first fixing section 480, may be conveyed along
the guide member and further subjected to fixing in the fixing nip
region of the second fixing section 490. As described above, by
carrying out fixing in the fixing nip regions of the first fixing
section 480 and the second fixing section 490, fixing performance
and image gloss can be improved.
[0220] FIG. 13 is a view showing the configuration of a fixing
device 530 according to a fourth embodiment of the invention. The
fixing device 530 includes a fixing section 540 and a pressure
section 550. The fixing device 530 carries out fixing onto the
recording paper sheet 32, on which the unfixed toner images 31 are
borne, in the fixing nip region which is formed between the fixing
section 540 and the pressure section 550. The fixing device 530 can
be mounted in the image forming apparatus 100, instead of the
fixing device 15.
[0221] The fixing section 540 includes a heating section 541, a
fixing roller 542, and a fixing belt 543 which is an endless-shaped
belt. In the fixing section 540, the fixing belt 543 is supported
around the fixing roller 542 and the heating section 541 with
tension.
[0222] The heating section 541 has the above-described heating
member 21. The heating member 21 of the heating section 541
includes the above-described heat radiating member 210, the heat
generating member having the heat generating layer 310, and the
inside securing member 218. The heat radiating member 210 contacts
the fixing belt 543 on the outer circumferential surface thereof so
as to transmit heat generated by the heat generating layer 310 to
the fixing belt 543. The heat generating layer 310 is composed of
the resistance heat generating element in which the paper passing
region heating section and the detecting section are electrically
connected in parallel, as described above.
[0223] The inside securing member 218 is configured by a
spiral-shaped member formed to be a spiral shape, and holds the
heat generating member having the heat generating layer 310 by
being in line-contact with a surface side of a thickness direction
of the heat generating layer 310 so as to elastically press the
heat generating member toward the direction moving closer to the
heat radiating member 210 and by allowing another surface side of
the thickness direction of the heat generating layer 310 to be in
surface-contact with the inside surface of the heat radiating
member 210. Furthermore, a heat generating element-side thermistor
545 is arranged around the circumferential surface of the fixing
belt 543 wound around the heating section 541 and detects
temperature of the circumferential surface in a non-contacting
manner.
[0224] The fixing roller 542 is a roller-like member having an
outer diameter of 30 mm, which is driven to rotate in a rotation
direction X around the rotation axis by a drive motor (not shown),
thereby conveying the fixing belt 543. The fixing roller 542 has a
three-layered structure consisting of a core metal 542a, an elastic
layer 542b, and a surface layer 542c, which are formed in this
order from inside. For the core metal 542a, for example, a metal
having high thermal conductivity such as iron, stainless steel,
aluminum, or copper, or an alloy thereof is used. Although examples
of the shape of the core metal 542a include a cylinder and a
column, the shape of the core metal 542a is preferably a cylinder
since the amount of heat generation is small. For the elastic layer
542b, a heat resistant rubber material such as silicone rubber,
fluorine rubber, or fluorosilicone rubber, is appropriately used.
Among them, silicone rubber is preferably used which is excellent
in rubber elasticity.
[0225] The material for the surface layer 542c is not particularly
limited insofar as heat resistance and durability are excellent and
slidability is high. For example, a fluorine-based resin material
such as PFA or PTFE, or fluorine rubber may be used. Alternatively,
a two-layered structure with no surface layer may be provided. The
fixing roller 542 may be provided with a heating section for
heating the fixing roller 542 in an interior thereof. This is to
reduce the rising time from when the image forming apparatus 100 is
powered-on until image formation is possible, and to suppress a
decrease in the surface temperature of the fixing roller 542 due to
heat transfer to the recording paper sheet 32 at the time of toner
image fixing.
[0226] The fixing belt 543 is heated to a predetermined temperature
by the heating section 541, and comes into contact with the fixing
belt 543 to heat the conveyed recording paper sheet 32 on which the
unfixed toner images 31 are formed. The fixing belt 543, which is
an endless-shaped belt, is supported around the heating section 541
and the fixing roller 542, and wound around the fixing roller 542
at a predetermined angle. When the fixing roller 542 rotates, the
fixing belt 543 is driven by rotation of the fixing roller 542 and
rotates in the rotation direction X. The fixing belt 543 is
provided to come into contact with a pressure belt 553 in a
pressure-contact region between the fixing roller 542 and a
pressure roller 551 described below.
[0227] The fixing belt 543 is an endless-shaped belt that has a
three-layered structure consisting of a substrate layer, an elastic
layer, and a release layer. The fixing belt 543 is formed to have a
cylindrical shape of a diameter of 60 mm and a thickness of 270
.mu.m. The material for the substrate layer is not particularly
limited insofar as heat resistance and durability are excellent,
and heat resistant synthetic resins may be used. Among them,
polyimide (PI) or polyamide-imide resin (PAI) is preferably used.
These resins have high strength and high heat resistance as well as
are inexpensive. The thickness of the substrate layer is not
particularly limited, and is preferably in a range of 30 to 200
.mu.m. In this embodiment, the substrate layer is made of polyimide
and has a thickness of 100 .mu.m.
[0228] The material for the elastic layer is not particularly
limited insofar as the material has rubber elasticity, and
preferably the material is also excellent in heat resistance.
Specific examples of such a material include, silicone rubber,
fluorine rubber, and fluorosilicone rubber. Among them, silicone
rubber, which is excellent in rubber elasticity and has
satisfactory heat resistance, is preferably used. The surface
hardness of the elastic layer is preferably in a range of 1 to 60
degrees based on the JIS-A hardness scale. When the surface
hardness of the elastic layer is within this range based on the
JIS-A hardness scale, deterioration of the strength of the elastic
layer and defective adhesion can be prevented, and defective
fixability of toner can be prevented. Specific examples of silicone
rubber having such properties include one-component, two-component,
or three or more-component silicone rubber, LTV, RTV, or HTV-type
silicone rubber, and condensation or addition-type silicone rubber.
The thickness of the elastic layer is preferably in a range of 30
to 500 .mu.m. When the thickness of the elastic layer is within
this range, the elastic effect of the elastic layer can be
maintained, and thermal insulation can be minimized, thereby
achieving power savings. In this embodiment, the elastic layer is
made of silicone rubber having hardness of 5 degrees based on the
JIS-A hardness scale and a thickness of 150 .mu.m.
[0229] The release layer is made of a fluorine resin tube. The
release layer formed on the outer circumference of the fixing belt
543 is made of a fluorine resin. Thus, the release layer is
excellent in durability, as compared with a release layer which is
formed by applying and baking resin containing fluorine resin. When
a release layer is formed by application and baking, an accurate
and expensive mold is required so as to a release layer with high
dimension accuracy. Meanwhile, when a tube is used, a release layer
with high dimension accuracy is obtained, even without using the
above-described mold. The thickness of the release layer is
preferably in a range of 5 to 50 .mu.m. When the thickness of the
release layer is within this range, the release layer can follow
fine irregularities of the recording paper sheet 32 while having
appropriate strength and ensuring elasticity of the elastic layer.
In this embodiment, for the release layer, a PTFE tube having a
thickness of about 20 .mu.m is used.
[0230] Next, the pressure section 550 will be described. The
pressure section 550 includes a pressure roller 551, a tension
roller 552, and a pressure belt 553 which is an endless-shaped
belt. In the pressure section 550, the pressure belt 553 is
supported around the pressure roller 551 and the tension roller 552
with tension. The pressure roller 551 and the tension roller 552
are rotatably supported between left and right side plates (not
shown) of the fixing device 530.
[0231] The pressure belt 553 is configured in the same manner as
the above-described fixing belt 543, and rotates by rotation of the
fixing belt 543 being in contact therewith.
[0232] The pressure roller 551 is a roller-like member that is
rotated in a rotation direction Y around the rotation axis by
rotation of the pressure belt 553 which is rotated by rotation of
the fixing belt 543. The pressure roller 551 has an outer diameter
of 30 mm. The pressure roller 551 has a three-layered structure
consisting of a core metal 551a, an elastic layer 551b, and a
surface layer 551c, which are formed in this order from inside. As
the materials for the core metal 542a, the elastic layer 551b, and
the surface layer 551c of the pressure roller 551, the same
materials as those for the core metal 542a, the elastic layer 542b,
and the surface layer 542c of the above-described fixing roller 542
may be used. The pressure roller 551 is provided with a heating
section 551d for heating the pressure roller 551 in an interior
thereof. This is to reduce the rising time from when the image
forming apparatus 100 is powered-on until image formation is
possible, and to suppress a rapid decrease in the surface
temperature of the pressure roller 551 due to heat transfer to the
recording paper sheet 32 at the time of toner image fixing. In this
embodiment, for the heating section 551d, a halogen lamp is
used.
[0233] The tension roller 552 is configured such that a silicone
sponge layer 552b is provided on an iron-alloy core metal 552a
having an outer diameter of 30 mm and an inner diameter of 26 mm so
as to decrease thermal conductivity, thereby decreasing thermal
conduction from the pressure belt 553.
[0234] The fixing device 530 is a so-called twin-belt fixing type
fixing device in which the fixing nip region is formed at a region
where the fixing belt 543 and the pressure belt 553 come into
contact with each other, and fixing is carried out in the fixing
nip region. In the fixing device 530, the pressure-contact region
where the fixing roller 542 and the pressure roller 551 come into
pressure-contact with each other with the fixing belt 543 and the
pressure belt 553 interposed therebetween becomes the lowermost
stream portion of the fixing nip region. Of the entire fixing nip
region formed at the portion where the fixing belt 543 and the
pressure belt 553 are in contact with each other, the lowermost
stream portion is a portion where the pressure distribution in the
conveyance direction of the recording paper sheet becomes the
maximum. As described above, by making the configuration such that
the pressure distribution at the lowermost stream portion of the
fixing nip region becomes the maximum, the fixing belt 543 and the
pressure belt 553 can be prevented from slipping at the time of
rotation.
[0235] The fixing device 530 is also provided with a fixing pad 544
and a pressure pad 554 so as to ensure a wide fixing nip region,
without increasing the size of the device. The fixing pad 544
serves as a first pressure pad that presses the fixing belt 543
toward the pressure belt 553. The pressure pad 554 serves a second
pressure pad that presses the pressure belt 553 toward the fixing
belt 543. The fixing pad 544 and the pressure pad 554 are arranged
to be supported between left and right side plates (not shown) of
the fixing device 530. The pressure pad 554 is pressed toward the
fixing pad 544 with a predetermined pressing force in a direction Z
close to the fixing pad 544 by a pressing mechanism (not shown). As
the materials for the fixing pad 544 and the pressure pad 554, PPS
(polyphenylene sulfide resin) may be used.
[0236] When the fixing nip region is formed by the fixing pad 544
and the pressure pad 554 which are not rotators, the inner
circumferential surfaces of the fixing belt 543 and the pressure
belt 553 frictionally slide on the respective pads. Then, when the
friction coefficient between the inner circumferential surfaces of
the respective belts 543 and 553 and the respective pads 544 and
554 increases, slide resistance increases. As a result, image
slippage, gear damages, an increase in power consumption of the
drive motor, and the like occur. In particular, in the twin-belt
system, these problems become conspicuous. For this reason, low
friction sheet layers are provided on the contact surfaces of the
fixing pad 544 and the pressure pad 554 with the respective belts
543 and 553. Therefore, the respective pads 544 and 554 can be
prevented from being abraded due to friction to the respective
belts 543 and 553, and slide resistance can be reduced. As a
result, satisfactory belt running property and durability are
obtained.
[0237] The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The present embodiments are therefore to be considered in
all respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description and all changes which come within the meaning
and the range of equivalency of the claims are therefore intended
to be embraced therein.
* * * * *